-I personally like darker ones, so I go here: http://dark.pozadia.org/category/Gothic/ ((Or various other sites like it.))
-If you like misc/other types, try here: http://pixdaus.com/ ((There's THOUSANDS, and they're all beautiful, but they're a b*tch to sort))
-If you're feeling adventurous, try the 4chan.org wallpapers thread (wg, or 'wallpaper general') but that site has a LOT of adult content, a good portion of the posters are trolls, and the wallpapers are hit or miss. It depends what people feel like posting that day. I never could get into 4chan myself, but it has it's occasional uses.
- Other than that, pick a topic you'd like as your wallpaper (being specific helps, but isn't really necessary) and google it. Then at the top left of the page, click the "images" link, which will show you only images related to your search. Then you can click "Show options" in the upper lefthand side of the page, under the Google logo, which will bring up a bar on the left side to help you refine your search. You can use that bar to only show large or extra large pics (good for finding desktops) or you can find pics by color, which is also useful if you don't really have a specific topic in mind. I apologize if you already knew how to do all that, but some people don't, so I figured I'd throw it out there anyway lol