 Last.fm
I didn't think this should've gone into Media Discussion because this is about a program about music, not the music itself.
Last.fm is a nifty little program/website that installs a plug-in into your preferred media player and keeps track of what songs you play on their website. It also suggests other artists/songs you may like based on others, and other stuff, such as generate lists like the one in my sig. The only real downside is that artists with the same name have the same page, like Mr. T (who does has some real songs apparently).
If you have one, post links to your profile and we can have happy fun friend listings. (Protip: click my list for the page) | 
