If you use XP, and have a flat panel monitor or a laptop, go get
this. Seriously. Now.
If ClearType is turned off, turn it on and fiddle with the settings. It's unbelievable how much of a difference good-looking fonts can make. I've always thought that one of the things about Macs that makes them so cool is how nice the text looks. Now I don't have to be so envious anymore.