Stock Photo website

I've been looking to round out my mammal card set for a while. While in training, I purchased 2 of the Audubon Society's pocket field guides to North American (wild) mammals. This is a great resource, but if we are starting with the general and moving on to the specific, shouldn't a mammal set include elephants, domestic cats, cows, monkeys, and, most importantly, humans? Here's a little sample of the free stock photos I downloaded at www.sxc.hu
with this project in mind:

This is a great stock photo site that allows you to search their database by keyword. The photos are free to download. I simply click on the photo to enlarge it, right click to "save as," and choose it's destination on my computer. From here, I can burn a disk or put the photos on my memory stick to print them out at any digital printing station. I print out 2 of each for reading classification cards. They can also be used for matching cards for very young children ... I plan on making sets that are matching by skin/animal, nose and mouth/animal, appendage/animal, mother/baby, etc. And some of the examples:

There are certain card sets that I haven't been able to compile through this site due to lack of photos - musical instruments being one of them. If anyone knows of some other free stock photo sites that might be useful, let me know!