You can do a search in android market for live wallpapers. You can also use an alternate market called slideme.
My list of favorite wallpapers:
-Live Aquarium (I love this one but huge battery hog)
-Earth Live WallPaper by unixseb (absolutely the coolest, makes the SuperAmoled pop with delight)
-VR Tunnel Lite..by MaxByte Studio LLC (Comes in as my second favorite, running it now!) (Runs a black screen with grid marks, so the black screen is not too shabby on battery!)
-Bubbles Live Wallpaper (Amazing Amazing Amazing, but HUGE HUGE battery hog, HUGE!)
-Leaf Bubbles Live Wallpaper by Livewallpaper Team (same as one above it, but it's leafs, huge battery hog)
-Zoomfield by Kaj Bjurman
-Quads by Kaj Bjurman
-Physx (very cool)!
-Nexus One Live Wallpaper by Andres Schmois
All are free. To apply, download, then go to wallpapers, click live wallpapers, and apply through there. Also many of these wallpapers have settings. For example, the earth one, you can change the earth to a soccer ball, you can change the speed of rotation, background, etc.
Enjoy but beware, they use battery!