This page contains a list of links to sites containing windows wallpaper, screensavers, and themes. Feel free to email me (tonysl@ihug.co.nz) with your own recommendations, but don't expect to see them here unless and until I have followed them and decided I like them.
Links to wallpaper sites
Wallpaper Heaven is a good place to start - they have links to every kind of wallpaper you could want (well, mostly). The main pages are low on graphics, so they load fast.
Mephisto's Animé Images has a selection of full-screen wallpaper from Japanese animation in three sizes.
ADV Films Media page has more of the same, from films they market, plus links to other pages on their site, including lots of images from videos, not necessarily wallpaper-scaled.
Stuff I've collected off the net
(I believe these to be in the public domain - however, if you own the copyright on anything listed here, please email me (tonysl@ihug.co.nz) and I'll remove it):