Learning Radiology: recognizing the basics. The website is good (and free), the book is significantly better (and pretty cheap), and the online quizes included in the cost of the book are fantastic for hammering concepts home.
If you are looking for how to actually ready them, I cannot emphasize enough the need to get behind a resident reading films. At my school there is a room where all they do is read Xrays, 100s all day long. I now dominate in X-ray interpretation. Im no radiologist, but comparable to even most of my residents, I can pick up things better than they can. I spent 8 days behind a resident.
I too looked for a text to orient me. I didnt find any that were particularly strong. Learning Radiology Website + 100s of films of Practice was the formula for me.