Occasionally when I have needed an image for a web site, or even just inspiration for a colour scheme, I have headed over to Stock.XCHNG, where there are hundreds of thousands of images. It seems Stock.XCHNG has new ownership in the form of Getty Images, and there has been a break away called RGBStock.com.
Obviously the number of images is lower at this time, but the site is easy to navigate, and a number of previous contributors to Stock.XCHNG have made the move over to RGBStock.com. The licensing of images is pretty liberal, even for commercial use.