Flaming Text is an awesome web site for fonts and banners that are saved as images (like my headers). I've used them for years, and they're great! (http://www.flamingtext.com)

KidsClick! Clip Art is a list housed a Berkeley, compiled by librarians, and made specifically for helping kids find clip art. This is one to recommend to students. (http://sunsite.berkeley.edu/cgi-bin/searchkids.pl?searchtype=subject&keywords=Clip+Art&title=Clip+Art)

Cartoon Machine is one that I might say is more for teachers than students. I didn't have time to read every cartoon that's been generated, but I worry about age appropriateness. I might just use this to make neat cartoons for my web site, to put on worksheets, etc, but I wouldn't recommend it to students just yet. What exactly is it? It's a place where you can design your own cartoons even if your drawing skills don't go beyond stick people. The characters and setting items are provided--you mix and match. Then, add a caption. Pretty neat. (http://www.iconbazaar.com/)

IconBAZAAR
has extensive web site galleries that would be useful to both teachers and students. (http://www.iconbazaar.com/)

Discovery School Clip Art provides decent clip art for educators and students. What I like about this site is it's clear copyright policy. It tells you exactly what to do (and not to do) with the images you use. (http://school.discovery.com/clipart/index.html)

FreeFoto.com This site contains beautiful photos for free and fair use. I wouldn't likely recommend a person use these on worksheets, as they might not copy well in black and white, but they could make neat graphics for a webquest. (http://www.freefoto.com/browse.jsp?id=100-0-0)