I wasn't sure if everyone was aware of this resource, so I thought I'd post it:
100% public domain clip art. The only problem is that it is in SVG format, so you'll need a program that can handle SVG and export it to whatever format you need. I use the GIMP for that purpose. It's also freely available:
Also, using the image from the menu bar on the gamechef site, I made a small gif to put on the cover of my game. I put it up on my website for anybody to use. It's in gif format.
Joe