I have just rediscovered WindowBlinds. It's amazing what a pretty skin will do for something. I hate that default blue look that XP ships with. The first thing I do when I get a new computer is change the theme to silver.
*UPDATE* I'm now using Style XP, which is much, MUCH better than WindowBlinds because it uses Windows XP's native theme machinery. Thanks, Eric! Also, SideBar is a great little freeware utility, except that it is currently consuming 83MB of my precious RAM. Download it and preview what Longhorn will offer. :)
Anyway, here's my desktop, now: