Aunt Minnie has lots of images and other information about Radiology. You have to register, but it's free, and it's a useful site. Check out the case of the day, but beware of the evil forums.
If you're looking for oodles of images, one of my professors set up an awesome site for CT (http://ctisus.org) that is filled with all kinds of information.
I liked www.learningradiology.com for my 3rd yr clerkship. Powerpoint presentations with questions. Would be useful for medicine and surgery clerkships since it does ask some good general medical questions in addition to radiologic ones.