Ian Writes: Understanding Comics: The Invisible Art, by McCloud. While this book claims to be about comics, many of the lessons within can be applied to game design and other forms of art. It also happens to be a comic book itself, and fun to read.Ian is correct, it's a great little book and I can easily see how most of it can be applied to games as well as comics. I did a little web searching on Scott McCloud and quickly came up with even more good stuff: Scott McCloud's Web Site including a blog and much more, Scott McCloud's TED lecture, and of course you can pick up your own copy Understanding Comics for $16.55 + shipping at Amazon.
Here is the Scott McCloud video from TED: