Good call on this post, as a contributer to both the payed and free world of stock photography and design... I know how it feels when I am asked permission for use and when I find poeple redistributing or even selling my work as their own!
If it hasen't been mentioned a few good resources are:
Stock Exchangewww.sxc.huThis is a free stock community with good caliber work- the usage restrictions are under the photo and range from free for website and non for profits to notifying the artist to getting their permission.
**Its always good to practice good manners and treat the work like it was your own- a thank you and I am using this comment goes a long way. People are generally understanding and will give their images away if you show them the beautiful art you have created with them to grace blog sites all over the internet!-
I know I am!
Another great free resource is
Morge filehttp://www.morguefile.com/Same edicate when using their work- We want our work to be used- just remember to practice common courtesy:)
See a good list of free and shared work here:
http://www.photoshoptalent.com/photoshop-links/Happy designing everyone
Hope this helps