Id highly recommend " The Photoshop CS Book for Digital Photographers" by Scott Kelby. Its extremely well written and I have learnt tonnes of great techniques from it. I actually understand the vast world that is photoshop now which is a miracle!
Here is a small quote
"So here it was, about four weeks before I would be flying up to New York City to teach a one-day seminar to more than 1200 professional Photoshop junkies. (Okay it was more like 1,160 pros, 42 people who just wanted a paid day off from work, and one total freak who kept asking me if i'd ever been to prison. I told him unequivocally, "Not as far as you know".)
He mixes humor with knowledge, its actually an enjoyable way to learn.
So thats my contribution.