Tisha B'Av and the Three Weeks
Halakha and Jewish thoughts on the meaning and observances of this period of mourning. From the Orthodox Union.
http://www.vbm-torah.org/3weeks.htm

Tisha Bav and Three Weeks in Sound
RealAudio classes about Tisha Bav and the three weeks leading up to it, including chanted versions of the Book of Lamentations (Eichah). From 613.org, a Hasidic audio website.
http://www.613.org/3weeks.html

Tisha B'av Basics
Simple overview of the history and observances. Features list of dates for upcoming years.
http://www.jewfaq.org/holidayd.htm

Tisha BeAv
Essays on the role of Jerusalem in Jewish life, the holiday from an educator's perspective, and an online quiz. From the Jewish Agency's education department.
http://www.jafi.org.il/education/FESTIVLS/av/index.html

Tisha Bav And The Three Weeks
Take a detailed tour of the Holy Temple, and discover how to observe this time of mourning. Includes history, current calendar, practical "How To" guide and insights into the significance of these dates from the wells of Chassidic wisdom. By Chabad.
http://www.chabad.org/holidays/3weeks/

Tisha B'Av and The Three Weeks
Laws and rituals, essays, poetry, and Talmudic insights on this period of mourning. From Ohr Somayach yeshiva in Jerusalem.
http://ohr.edu/yhiy.php/holidays/tisha_bav/

Story of Kamsa and Bar Kamsa
The classic story that gives the reason behind the destruction of the second Temple.
http://www.jewishmag.com/12MAG/KAMSA/kamsa.htm

Tisha B'av Resources
Features three PDFs dealing with customs and observances, text study of a mishnah in Masechet Taanit, and a Midrash of Megilat Eichah.
http://www.hillel.org/jewish/holidays/tishabav/