Best Bets
1. Flickr – Under Creative Commons you can use a lot of the images on Flickr, just make sure you give the appropriate credit.
2. Stock.Xchng – Big collection of free stock photos, some have weird license terms, but the collection and variety is pretty amazing.
3. MorgueFile – The amount of photos is a bit limited but the quality is really quite high.
4. Stock Vault – More of an exchange for images between photographers but you can snag some free images from here even if you’re not a photographer.
5. EveryStockPhoto – Search engine of free stock photos. Very useful for deep dives looking for images.
Hit or Miss
6. FreeRange – Nice collection of good quality images.
7. FreeFoto – Collection is a bit limited, but occasionally you’ll find exactly what you need.
8. Pixel Galerie – Site isn’t in English but isn’t that hard to navigate and does have some nice pictures.
9. Unprofound – Decent collection in both size and quality, but nothing too amazing.
10. Public-Domain-Photos.com – A few thousand images only but you might stumble on what you need.
Longshots
11. Google Images – You can always search images on Google and then contact the site owner of any images that come up to see if you can have permission to use the image. Not very likely to work, but you never know. Your odds will be better if you’re non-commercial.
When All Else Fails…
12. If none of those worked out then I suggest iStockPhoto. Pictures are super cheap and really nice quality, but not quite free 
Thank you for this list, it will be really helpful…