I’d say about 99% of the websites that actually offer wallpaper downloads are full of spam, spyware, popups and any variety of malicious content. It’s better to use good ol’ google.
Just type the kind of stuff you’re looking for in the search bar, click “Images” and check out the pics you like. Then just right-click, ‘Set as Background’ on the image.
if you’re not sure what to search for, just type generic stuff like ‘cool wallpaper’ until you get some idea of what you want.
The best background i made was pretty simple, unique, and it could fit my own style. You need a digi-camera though. What you do is put a cool background on your wallpaper, then take a picture (no flash) of your monitor, maybe the surrounding desk space included. Then upload that pic, and make it your wallpaper. Then take another pic of your monitor, and repeat the process a few times. If you’ve captured items on your desk in the images, it might be funny to switch their positions in each pic. It turns out pretty cool.