1) StockFreeImages.com - With over 570K photos for download, you can probably find most of what you need here.
2) stock.xchng - Very popular free image site with almost 400K free images to choose from.
3) FreeDigitalPhotos.net - Has lots of original photos for free download.
4) StockPhotosForFree - With over 100K free high-quality photos.
5) RGBStock - Has a collection of 72K free images.
6) Kozzi - Over 50K free images for download.
7) StockVault.net - Download over 32K images for free.
8) MorgueFile - Has in-house photographers who contribute to their extensive collection.
9) FreeRangeStock - Smaller collection but higher quality images for free.
10) FreeStockPhotos.biz -Many unique photos as well as other kinds of photos for free.
11) Gimp-Savvy - Extensive collection of 27k public domain images.
12) PublicDomainPictures.net - Another great resource of more than 23k public domain images.
Another wonderful free image site is PhotoXpress. Go to EveryStockPhoto's "advanced search" function and uncheck all the sites except PhotoXpress. Then do a search for the images you require. You'll find many more free images.
Would love to hear if you know any better sites.