do you use IE? if you do, get the latest Firefox Beta (4.0 beta 9) and experience an awesome browser
(mozilla fanboy, sorry)
you could try Spotify, web streaming music, or stuff like GIMP and Xara for some kooky image editing.
and, if you're into making your desktop LOOK good as well as run good, get Rainmeter
awesome alternative to the crappy windows gadget things, and it uses next-to-no resources.