I was getting tired of the standard Apple wallpapers on my iPhone and I haven't taken any great photos recently to use for my iPhone wallpaper, so I found out that to get iPhone wallpaper, you can:
Download iPhone wallpapers
Create wallpapers yourself
Take pictures to use as wallpapers
Download iPhone wallpapers
If you want to download iPhone wallpapers, here are some sites that I found are good:
I've also included a gallery of a few that I made below.
Create wallpapers yourself
If you know a thing or two about Photoshop or another image editor like Paint Shop Pro, then you can easily make iPhone wallpaper yourself. All you do is create an image that's 320x480 (320 pixels wide by 480 pixels high) and then create away or else paste in a photo or something.
Take pictures to use as wallpapers
And, as always, you can take photos yourself wth your iPhone and them set them to be your wallpaper by going into the Photos, choosing your Camera Roll, choosing which picture to use, then click on the icon on the lower left to choose the option to use it as your wallpaper. Easy.
That's also how you kind of get wallpaper that you've downloaded (with your computer, not the iPhone itself) onto the iPhone... put those photos into a photo gallery and then set up your iPhone sync in iTunes to upload that gallery to your iPhone.
My Gallery
Feel free to save these and use them - just do not distribute or sell them, please.