iOS Wallpaper
There are a number of wallpaper apps on the App Store which promise to have the best or largest selection of wallpaper images. I'm sure some of them are great but none of them can compare to the selection on google.
Google's advanced image search parameters make it easy to find images with the right dimensions. Just specify the size and search for "wallpaper", or something more specific if you have something in mind.
- iPhone 1,3,3GS (320x480) 924,000 results
- iPhone 4 (640×960) 196,000 results
- iPad (1024×768) 4,460,000 results
If you are also a Dropbox user, consider browsing for wallpaper on your desktop, transferring it to a folder on Dropbox, then browsing this folder on your iOS device when you are in the mood for a wallpaper refresh.