I've been searching through stock.xchng for a while now.
stock.xchng - the leading free stock photography site
They're a free membership site with photos ranging from totally restricted to for free - no restriction uploaded by users. They have an advanced search tool where you can specify Restricted OK - Yes, No or partly.
If you search No the majority of images come up with the notifications "Usage Royalty free, no restrictions", and, "Restrictions: There are no usage restrictions for this photo."
However I will usually check the profile of the uploader to make sure they took the photo and if there are any additional notes like "I would love to know if you use my photo!" or "Please comment and critique me, so I can take better pictures. And I would be happy to know how my pictures are used." and I try to make sure I note this down and return a reply to them so they are happy and uploading many more photos free of restriction. There's also a rating system and comment area which is only polite to use since they are supplying material freely.
Additionally there is a Restriction Free Stock Exchange Club! user blog that lists many of the uploaders who grant free use on their photos.
stock.xchng - a51media's blog - Restriction Free Stock Exchange Club!
Anyway, I hope this is is of some use.
Outré