O'Reilly Media | Mac OS X Leopard: The Missing Manual
If you are new to Macintosh computers or simply upgrading to Leopard (OS X 10.5), you will save yourself a lot of time and effort by investing in David Pogue's "Missing Manual - Lepard Edition". He is wicked smart, funny and hip to all the insider tricks and tips. In short, he is the computer professor I wish I had in college. If you are still skeptical, check out his column in the New York Times "Circuits" section on Thursdays. P.S. - I am actually reading this from cover to cover.