There are several sites that I have visited online that offers cool and creative ideas for Halloween costumes. I have tried making one last year and sent it to my nephew who lives in Canada. He was very happy to have it.

These are the sites for costume ideas:
1. Coolest Homemade Costumes (http://www.coolest-homemade-costumes.com/)
I think you have the motivation and creativeness so this site will aid in inspiring you to make a great Halloween costume.
You will find thousands of homemade photos and how-to-tips to help you create your own costume. This site also has the largest collection of "makeable homemade costumes" through the submissions of visitors to the site. They categorized these ideas into animal costumes, at-work costumes, baby costumes, celebrity costumes, character costumes, spooky costumes and many more.
You will find an image below to see one of their Halloween costume ideas.

2. Costume Idea Zone (http://costumeideazone.com/)
You will also find a lot of unique and creative costume ideas at Costume Idea Zone. You will also find very helpful tips on how to make creative Halloween Costumes without spending too much.
These are examples of unique costume ideas:
Skill Crane (see image below)
Aquarium
Popcorn
Rubik's Cube

One book that is great as a reference for making your Halloween costumes is the "Creative Costumes and Halloween Decor". This book is designed within the three basic styles: tabards, gowns and full suits. You will also find her some accessories ideas like wings, capes, skirts, and head wear. You will also find some detailed information in making collars, gloves, spats, and face painting instructions to personalized your costumes.

My mother is an excellent seamstress and has always made her kids and grandchildren's Halloween costumes. I have found that for kid's costumes, SB Kids has a great selection. You can sign up with them to receive their catalogs or visit them online. They also have great toys that encourage imagination as well.

For kids and adults I recently looked at a catalog from Halloween Express. They had some cute costumes. I will have to admit that I thought some of them were a bit trashy. They have catalogs and a website.

I also look at pattern books at stores like Hobby Lobby or Hancock's Fabrics. You can also find some great idea on some crafting sites and blogs. One of the best places I have found for inspiration for costumes is eBay and/or consignment stores. I think used items have some real character and can give the best inspiration.

Of course, not only that. The best ideas can also come from movies, T.V., books and even items from around the house. I remember once this lady was having a hard time deciding what to be. We worked in a grocery store at the time. I looked over and there were bags of Doritos. I said, go as a bag of Doritos. Well, she did and won 1st play in the contest. She made her outfit.

As far as books for Halloween costume ideas, I suggest you buy Halloween Costumes by Singer Sewing Reference Library sold at amazon.com for just $5.17 for brand new and as low as $0.01 for the used books. This costume books contains an easy to follow guide and images for sewers to compare with his/her chosen costume. Another thing I found interesting in this book is the fact that it covers all the aspects of costume design from head wear to shoes.

Furthermore, this instructional book provides the most commonly used styles by sewers such as tabards, gowns, and full body costumes. Accordingly, "this book teaches all the necessary sewing techniques to make simple, scary fancy-dress Halloween outfits for both adults and children."

This book have great customer reviews, receiving 5 star for 2 users.