A big chart of the characters in Doonesbury and their connections. PDF file.
Below is a JPG, but you need the file above to be able to read it.
... This is obviously for Doonesbury fans, but I think pretty much anybody who like satirical cartoons should read Doonesbury, particularly in collections. It is not for really casual readers, but it pays off in spades, while often subtle, the humor is sometimes of the highest class.
(BTW, the newest collection in Kindle format, is high-res and in color, grand for use on iPad or Kindle Fire HD.)
BTW, I have written to the Kindle team and suggested an extra kink in the programming for Kindle comic strip books. They've made it so you can see a strip in full screen by double tapping on it. This is great for middle-aged eyes, and the scanning is really high quality. But then you have to close it and double tap on the next strip to go forward. I've asked them to enable simply tapping on the right of a full-screen strip in order to go to the next strip, this seems to me to be the most helpful and natural way to read them.