I was looking for a few new advergames to talk about here (they really have become a phenomena) when I ran across one 'game' that is more serious than most. MTVU has lauched a site called Pos or Not where they encourage you to try to guess who has HIV and who does not. The site is co-sponsored by the Kaiser foundation and it really forces you to look at what stereotypes you may have about HIV.
This site really encourages you to show the site to your friends. It does well with its call to action and does its best to shed light on a terrible disease.