I know you sick fucks should have fun with this game.  I've played it once through so far and didn't manage to exterminate all of mankind with my virus, but I plan to have a go at it again.

http://armorgames.com/play/3189/pandemic-ii

I have a few times... it was fun.

Lucas, what was that nuclear annihilation game you posted ages ago?

http://www.introversion.co.uk/defcon/