20th Anniversary of World AIDS Day.
World Aids Campaign & World Aids Day.org are the two that I'm involved in.
The first site's theme is leadership, and they have a pledge you can take. The second site is mostly based around the UK but also has a special campaign going on for people who have MySpace or Facebook accounts.
Apart from that, you can read about the history of World Aids Day on Avert, which also covers pretty much everything to do with AIDS, including statistics, the location of test centers, steps to take to prevent getting AIDS, etc.
Finally, the UN AIDS site has a ton of messages from world leaders, a DVD of short seven-minute clips made by people around the world talking about how they're combating AIDS and a special speech by Dr Margaret Chan about AIDS in Africa and how it affects women.