If you ever wanted an easy way to study how lots of different games in all sorts of genres handle real-time collision detection, you're in luck: writer Chris Wagar has established a Flickr gallery filled with 450+ images of hitboxes.
There are a few duds in the album, but the vast majority of the images showcase how the developers of everything from Super Mario Bros. to Half-Life structured the collision systems in their games.
While it's a bit tricky to dig into any one set of images since the sources aren't listed (some appear to be captured from behind-the-scenes dev footage, while others look to be straight screencaps) it's a neat thing to scroll through and see how different devs decide what's "real" and what's not.