Dreamstime is a great resource for web designers. Besides photos there are lots of images what you can use in your designs or use on web pages as background images.
Here are few of my favorites.
I love to follow web design trends in design blogs, and as predictions for 2010 have said, the retro and grunge style is here to stay. It's obvious from Dreamstime illustrations as well. Lots of great retro and grunge images. Beginning with highly stylized collages and ending with simple natural textures like of water or fire or wood. Or just an image of old paint peeling from wall. All very useful for designs.
And of course it would be unfair not to mention all professional vector designs, floral designs and abstract art.
Photo credits: Ekaterina Chirikova, Freesurf69, Dmitriy Karelin, Jon Helgason, Konstantin Sutyagin, Luba V Nel, Marilyn Volan, Pavel Losevsky, Ramsin Eiwazpour-adeh, Rolffimages, Rudchenko, Sandra Cunningham, Leigh Prather, Solarseven, Katya Triling, Yuri_arcurs.