Tufte is great, but he's extremely heavy and a bit dated. He is about 80% brilliant 20% completely missing the point. It's very strange.
If you are looking for a smaller book I've found the WSJ Guide to Information Graphics by Dona Wong to be pretty decent and pretty straight forward, and it's about 100 pages. It's not too focused on finance either, although that's what I got it for (I do front end development for financial analysis company - lots of charting).
http://www.amazon.com/Street-Journal-Guide-Information-Graph...