I'm just finishing up SQL Server 2008 Query Performance Tuning Distilled by Grant Fritchey and Sajal Dam and overall I've been with impressed with the book. I think it covers all the major topics and goes into a reasonable level of detail, the kind you need to know to solve the problem. As much as I like the book I'm not sure how approachable it will be to true beginners, but to be fair there's no easy way to learn all the stuff you need to solve performance problems. For the rest of us it's a great reference and tutorial and I definitely learned a few things I had somehow missed, easily worth the $35. In my view this is the one performance book you should own right now and the one I'll be recommending to my students.

Bias disclosure: Grant is my friend, works with me on PASS stuff for free and some for pay stuff for JumpstartTV. I don't think that influenced me here, but fair to let you know.