http:wpclipart.com (Personal and Commercial Use)
http://www.clker.com (Personal and Commercial Use)
http://iconbug.com (Personal and Commercial Use)
These are mainly icons for use on blogs and websites.
Stock Xchng Photos
http://www.sxc.hu (Personal and Commercial Use)
Public Domain Clip Art
http://www.pdclipart.org (There is No Warranty)
Free Images Collection Photos
http://freeimagescollection.com (Personal and Commercial)
Please check individual sites for usage requirements and restrictions on commercial use as they vary considerably.