Gamewallpapers.com is good if you want video/computer-game related stuff.
Wapers.com is a big general-interest wallpaper site, though their content is rather scattershot.
Moved to IMHO.
General Questions Moderator
www.xpthemes.org is good. You can also get boot screens and logon screens for Windows XP there.
IMO VoodooFiles has the best and most current selection of 3D screensavers.
Also try these out:
Wow. What a great site!!
www.webshots.com is ok
They used to be awesome, then they changed things up a bit. Now they charge a fee to download more than 5 images a day.