The  biggest problem I’ve found with free stockart sites is that their search engines are horrible and/or they have a zillion clicks to get to the pictures through ads.  You search for something like “computer keyboard” and the search turns up everything from pictures of a blue platypus (yea, Agent P) to photos of barn doors. After alot of searching and trial and error, here are some of the better ones I’ve found:

FREE:

http://pixeldef.com (personal use only – see their legal page)

http://freepixels.com

http://freefoto.com

http://www.sxc.hu/

http://urbandirty.com/gallery/ (GREAT textures for free)

 

CHEAP:

http://istockphoto.com (of course)

http://www.veer.com/

http://www.bigstockphoto.com/

http://us.fotolia.com/

 

Most of the time it is generally better to pay something for them, even if it’s just a small amount, just to save time and effort.  The free ones are out there if you look hard enough, though.  Good Luck!