Yesterday I was looking for iPhone wallpapers, as I wanted to have something new and nice on my iPhone.
Here are some of the websites I have been browsing:
iphone-wallpapers.us
iphone-wallpapers.net
320×480
deviantart – 370 iPhone-wallpaper collection
Of course you can crop and resize any image, it should just have a width of 320 pixels, and height of 480 pixels.
Place your desired wallpapers in a new folder, and set it up to sync with iTunes.
Cool! Or you can transfer the wallpapers yourself via SFTP
It’s easier and it doesn’t mess up your photos 
An obvious omission to that list is InterfaceLIFT which has a massive collection of hand selected wallpapers, including a section devoted to 320×480 pixel iPhone / iPod Touch wallpapers.
they even have a spiffy Mobile Safari version of their site:
http://iphone.interfacelift.com/
or the regular site:
http://interfacelift.com/wallpaper/
(also a great source for nearly any resolution, particularly high resolution widescreen stuff)
680 iPhone Wallpapers (320 x 480) http://www.mobilevina.com/themes/themes-cho-dien-thoai/