Here's a few sites where some free textures and/or stock images can be downloaded...

http://www.imageafter.com/textures.php

http://www.textureking.com/

http://www.cgtextures.com/

http://mayang.com/textures/

http://texturez.com/

http://urbandirty.com/

http://www.sxc.hu/

Cheers

Ken