After I read your question, I sat and thought for a bit.
There can be lots of fluff to this type of question, but I thought to myself 'what is at the core? What is the foundation to being a good person?'

I believe that the core and foundation to being a good person is the capability of empathy. To see beyond your own world... your own needs and wants, and be there to help others. That to me is what makes a person good. To understand what another is going through. To be there not just for yourself, but for another. That is the basic structure of good.

So, what would be the opposite, or bad? Selfishness. Not being able to understand how the other feels. At the core of bad would be the definition of a sociopath.

I puttered around on the internet and found an interesting discussion. Rabbi Manus Friedman who is a chassidic philosopher has a nice little video about What makes a 'good' person? I found his discussion with Michael Kigel to be enlightening. Here is the link to the video. Enjoy.

http://www.chabad.org/multimedia/media_cdo/aid/676151/jewish/What-Makes-a-Good-Person.htm

I've actually spent a lot of time thinking about and defining "evil" and hadn't really thought too much about what it is to be "good". I'm a Christian and being good is a simple answer with complex implications that can take a life-time to partial understand. Still, I often talk about what evil is (in discussions of sin) and just use the antithesis to describe good. So this question gave me pause to think, thus my late response.

Once again, I pondered upon what is evil to understand what is good. Some people claim an inability to find any absolute answer. Particularly in ethics, some claim that it is impossible to come up with an impartial/unbiased ethical system because it is impossible for us to be perfectly impartial/unbiased. I'm going to ignore the skepticism and just focus on the root of what makes someone evil or good.

The root of evil is rather simple. And understanding it makes understanding good easier. But it may take some time to convince people, because upon self-reflection we come to realize how evil we really are or could be.

Evil is often confused with cruel. Cruel, while quite possibly evil, has more to do with the absence of empathy for someone else. Evil in its most basic form is selfishness. If you take the stereotypical villain and everyone's favorite super hero and compare them, what makes them different** (see side note). You could say that the villain is cruel, greedy, mean. He is cruel because he doesn't care about anyone else's feelings, only his own. He is greedy because he wants stuff only for himself. He is mean because he is protecting himself. All of them are self interests. Why does someone steal? for themselves. Why does someone murder? for themselves. Whether it be perverse pleasure or some kind of personal gain, in the end its just for your self. Evil is pure selfishness. To further support this, look at it's antithesis, the hero.

The hero is the hero because she is willing to do anything to help someone else. That is why she is considered good, because she puts the well-being of others above her own. The hero is selfless. If we look back throughout history, through any culture, selflessness is always considered a virtue. Heroic deeds passed down through centuries are not deeds of selfish desire, but of selfless sacrifice or love***.

So the answer to your question, "what does it mean to be a good person?", is be selfless. To be a good person is to do onto others as you would have them do on to you.

side notes:
** (enemies are not necessarily villains. We like to think of our enemy as the bad guy, but our enemy in not necessarily evil. Often they are not at all. Villains are those who who make it their life's goal to prosper themselves at the expense of others, or to make others suffer simply for the pleasure of it.)
***(True love is unconditional. It is selfless. While lust is selfish.)

My answer here is going to be biased by my own Buddhist beliefs and philosophies.

The only person that I have the right to judge is myself. I cannot tell you what makes anyone else good or bad, only how I see it in relation to myself.

I strive every day to be a good person. It's often a fight. I practice mindfullness and compassion. I forgive the people who have hurt me, and try to be understanding of their difficulties in life. I try to follow the noble eightfold path (right view, intention, speech, action, livelihood, effort, mindfulness and concentration/meditation). The easiest way I can explain following this path is that you're to do those things in the way that your conscience says is right, in a way that creates the least harm.

I find view, mindfulness, meditation and livelihood easy, and sometimes my Catholic past will make me feel guilty for that, because I subconsciously equate personal sacrifice with being "good". I find intention to be a middle ground. I don't tend to have bad intentions, so that should be easy, but I wonder about my subconscious sometimes. Speech, action, and effort are more difficult. It requires me to stop and think before speaking and doing things sometimes. Words can't be unsaid - what you put out into the universe affects people, and it's so easy to say something unintentionally that really hurts someone. Action and effort are a little easier, as for the most part they require a thought process too, but sometimes I do thinks unthinkingly, and I try hard to stop myself and be considerate and aware at all times, to watch for someone who needs a door held, for example, and not just quickly brush through, or something as simple as being conscienetious enough to return phone calls and emails promptly and not be late when I'm meeting someone, to consider the people around me to be as important as myself, and think about how what I do will affect them in one way or another.

I try, but I'm human, and so imperfect. But I hope I am getting closer to "good" over time :)

What Does it Mean to be a Good Person?
Surprisingly (or maybe not), this question is not as simple as it looks. In the US we often confuse being good with being successful, and this, to many people, means being financially successful. This notion took a knock when the American public learnt about Bernie Madoff and the obscene profits, and mistakes made by our bankers and financial experts, and the attendant suffering of ordinary hard-working people.
My answer, and any answer to the question contains my personal opinion, as will any honest answer. A good person, in my opinion, does not lock himself away and preach goodness from an ivory tower. A good person may be rich or poor, successful or obscure, but as long as he does his best to improve the lot of others, he is ‘a good person’. Please consider ‘he’ as applicable to both sexes.
Examples, in my book, range from aid workers to honest politicians to ordinary men and women who strive to provide comfort, guidance, and friendship to their families and peers. Examples range from Mother Theresa and Nelson Mandela, through Joe Blow, the janitor who works hard, stays cheerful, and helps his family achieve a better life.
There are many definitions of ‘a good person’. Go to www.askjeeves.com, and ask the question as a starting point. Philosophers, religious persons and atheists will give you good answers – if they are good persons.

it is open question and everyone response by his/her own thinking and perceptions about good person.
for me good person means;
respectable by those who know how to respect
lovable by those who know the meaning of love
careful for those who know how to care others
likable by those who linked too
who is sincere with him/herself
know what's wrong and what's right
don't blame others for faults or mistakes due to his/her own reason
face the reality
and most importantly believe on the statement
'I am responsible and I can do'
Thank you

@mar7, deep down, those people had to know they weren't doing anything truly "good"....or maybe certain (sadistic?) people have their own personal version of what "good" is......their own version of what "right" is---but even when that's the case, deep down you have to know with hatred in your heart, you can't be doing any REAL good. but arrogance, lies, swearing-those are human traits or more like human habits....those things don't mean a certain person is bad because they do those things.....and as for swearing being bad, that's actually more of society's view on that, and not really an individual opinion/actual fact.and it's really not as simple as being good or bad either..."there's a little bit of good in the worst of us and a little bit of bad in the best of us, so none of us-good or bad-have the right to judge any of us" ..... what makes a person truly evil? i can't even figure that out.... because like i said, it's sort of not that simple....but to me, being a good person is as simple as treating others the way you want to be treated, loving everybody (you don't have to like the things they do-but you should still love them) and helping other people. besides if you do that, you feel good...and feeling good is something i'm pretty sure hitler didn't feel....being so filled with hate. . i think if you feel truly happy (not that bitter, vengeful sort of happiness-but REAL happiness) , then you're on the right track.

There is no definitive source you can appeal to for an answer, no formula you can apply. Various religions claim to have a divine revelation that can be treated as a definitive answer, but those answers conflict with each other, so at most one can be correct, and there is no mechanism for determining which. (It's also possible that none of them are correct.)

I look at the question operationally: why do you care if a person is good or not? What difference does the distinction make? I can make the distinction between people who are "splink" and people who are "non-splink", but if the only way to distinguish is to ask me, you wouldn't bother with the distinction. If, on the other hand, people who were splink would be handed $5 next Tuesday, and people who were non-splink wouldn't, the distinction would now matter a great deal.

So... what differences are there between good people and non-good people, that you take the trouble to ask? I can give you a tentative and very incomplete list:

* Some say that "good" people get an afterlife; those who aren't get no afterlife or a bad one. This is clearly a distinction that matters a great deal to people, but there's no proof that it's real, and some reason to believe that it isn't. You can chalk this up to a matter of faith: if you want to believe it, you may, and that basically ends the conversation right there.

* Good people are people you want living around you. They have properties that make them good neighbors and family members. The definition varies from person to person, but various properties (helpfulness, generosity, trustworthiness, politeness, etc) figure prominently.

* Good people also refrain from doing many things (murder, theft, rape, lying, causing pain). These things are more or less universal, regardless of religion or culture, though the details vary from group to group. (Owning slaves was once considered a good thing, and even today people countenance abuse of animals that many would consider "not good"). In many ways, this negative definition of goodness is dominant: a person can easily be considered "good" just for keeping to themselves, but violating one of these other principles puts them unquestionably and easily in the not-good category.

* Good people make "good" decisions. There are a lot of difficult corner-cases here, like the famous "trolley problem": if a train were running out of control, would you divert it onto a track that would kill only one person and away from five others? Would you push one person in the way of the train if that would stop it? People often give different answers, even though from a simplified perspective they are the same: one person killed to save five. These are usually treated as exceptional, though in many ways they are an everyday occurrence: you could right this instant give all of your money to save other people, with measurable effects. Arguably, that means that practically nobody is a good person.

For these reasons, I consider the category of "good" so fuzzy as to be essentially meaningless, from a philosophical vantage point. That doesn't mean it's impractical; far from it. Most people, most of the time, more or less agree about most actions: feeding your family good; kicking puppies not good. It doesn't really require a whole lot of thought, just an adherence to cultural norms, and many of those are universal.

The rubber hits the road when they're not universal, and while people crave a definitive answer for the reasons I listed above (they want to be good, and to give other reasons people to be good), I don't think definitive answers will ever exist. I think that the notion is literally meaningless, a heuristic shortcut for a complex world. Finding better answers means finding better questions.