There are lots of wonderful wallpapers on http://www.applemacvideo.com/articles/free-wallpaper-theme.html (
this site). You can free download those wallpapers for your iPhone 3G, iPod touch, iPod... As shown below, those wallpapers are classified by theme style, contains Cartoon Picture, Super Star, Nature View, Art work, Game Photo etc. You can find those you are interested in easily.
Cartoon Picture:
Super Star:
Nature View:
Art Work:
There are still many other style wallpapers.
Get more http://www.applemacvideo.com/articles/free-ipod-iphone-wallpapers.html (
Free iPhone Wallpaper here).