Jewish Holidays are observed in commemoration of biblical events in the Torah, most often with prayer services, festivals, or feasts.
Shabbat (Sabbath)
Shabbat is the Jewish day of rest, observed from sundown on Friday night to sundown on Saturday night.
Chabad.org: Shabbat
Aish.com: Guide to the Laws of Shabbat
The Orthodox Union: Candle Lighting Times for Shabbat
The Jewish Outreach Institute: Shabbat - The Sabbath
Tot Shabbat: Shalom Shabbat Shalom Song
Siddur Audio: Shabbat Services Audio
The Big Jewish Holidays
Rosh Hashanah
Rosh Hashanah is the Jewish New Year and the beginning of the "High Holidays", also known as the "Days of Awe", when Jews reflect upon the previous year.
See Mahalo's Guide to Rosh Hashanah
About.com: The Jewish New Year
Judaism 101: Rosh Hashanah
All Recipes: Rosh Hashanah Recipe Collection
Yom Kippur
Yom Kippur is known as the "Day of Atonement". Jews the world over will fast for 24 hours as an act of repentance.
Wikipedia: Yom Kippur
MavenSearch: Yom Kippur Guide
American Jewish Committee: Yom Kippur Audio
Slate Magazine: Improving on Yom Kippur
Bible Gateway: Leviticus 16 - The Day of Atonement
Chanukah
Chanukah is the "Festival of Lights", an eight-day holiday commemorating the burning of oil seven days longer than expected, as described in the Talmud.
Chabad.org: Virtual Chanukah
Midrash: Hanukkah
Hebrew Songs: Chanukah Song Lyrics in English and Hebrew
All Recipes: Hanukkah Recipe Collection
Judaism 101: Virtual Dreidel Game
Seeqpod: Adam Sandler's "The Chanukah Song"
Purim
Purim is a celebratory holiday marking the thwarting of Haman's plan to commit genocide against all Jews. This story is read allowed twice from the Book of Esther.
Aish.com: Purim Basics and Activities
The Orthodox Union: The Mitzvot of Purim
National Jewish Outreach Program: Purim Night Megillah Reading
Gratz College: Purim History
Lag Ba'omer
Lag Ba'omer is celebrated on the 33rd day after Pesach to celebrate the ending of a plague described in the Talmud.
The Orthodox Union: Celebration of Lag Ba'Omer | The Mystery of Lag Ba'Omer
National Jewish Outreach Program: Lag Ba'Omer
Haaretz.com: The Fires of Lag Ba'omer (Iyyar 22, 5767)
The Not-Quite-So-Big But Also Very Important Jewish Holidays
Tu B'Shvat
Tu B'Shvat is the Jewish New Year for Trees. This is a day of nature appreciation; trees are frequently planted and fruits eaten.
Aish.com: Tu B'Shvat
iSolomon Holiday Central: Tu B'Shvat
Torah.org: Tu B'Shvat - The New Year For Trees
Tisha B'Av
Tisha B'Av takes place in midsummer (on the 9th day of Av, in the Hebrew Calendar), and is a national day of mourning in rememberence of the destruction of Jerusalem's first and second temples. These events took place on the same day over six centuries apart.
Wikipedia: Tisha B'Av
The Orthodox Union: The Ninth of Av | A Chronology of Destruction
Judaism 101: Tisha B'Av
Hillel: Tisha B'Av
About.com: About Tisha B'Av
Chabad.org: Tisha B'Av and the Three Weeks
Rosh Chodesh
Rosh Chodesh is Hebrew for "Head of the Month", and is observed at the appearance of a new moon, which is the beginning of a new Hebrew month.
Jewish Virtual Library: Rosh Chodesh
Chabad.org: The Laws of Rosh Chodesh
MyJewishLearning.com: Rosh Chodesh - The New Moon
Hebrew for Christians: Rosh Chodesh - The Gift of the New Moon
Ritualwell.org: Rosh Chodesh Prayers and Poems