Far and away, this is the best book I have found on learning things Mac. It's written by Jim Heid. I've checked it out of the library a couple of times, but it is so good, I think I'll actually break down and buy it, and I don't do that very often.
Or, I may wait to pick up Heid's "The Macintosh iLife '09" which I see is now available on Amazon. Of course, I'd need to buy the iLife '09 suite from Apple.
In the short span of the first 72 pages of this 420-page, oversized book, I have picked up far more tips than all of the other books I've read combined, and I'm still in the iTunes section! It's super-easy to read. Two pages per topic makes it a snap to pick up and put down. If you have felt a little frustrated that you are not using the software programs provided in the iLife suite to their maximum effect, this book is for you.
The Portable Genius series is also good. Damn, there are a lot of books out there. Granted, I haven't read them all. Who's got time? But these two series of books seem to be easily above the rest of the crowd.