If you're just starting out and refining your skills, a good place for free stock images is
stock.xchng - the leading free stock photography site. You have to sign up as a member, it's free, and then you have access to download images. Note that there are different types of licenses provided by the photographers: there's the basic license that's free for personal and commercial use, and then there are some that ask that you notify the artist if it's being used somewhere, others require permission upfront. I found this to be a great resource when I was a student and needed access to photos for projects.
License Terms