I used to swear off desktop wallpapers, because they always seemed to be a burden on the system. Advances in technology, or maybe just competence on the part of OS makers, has rendered the impact of using an image as your background moot.
The excellent Smashing Magazine has a post, More (Really) Stunning Desktop Wallpapers, and it really lives up to its name. My only problem now is picking which one to use!
I used to avoid wall paper as well. A while back I relented though. I use pictures I have taken myself. They are not always the best or most amazing pictures but they are meaningful to me. One laptop has a beach picture from the town where I was born. My main laptop has a picture of a very cool waterfall I saw in Iceland.