I just finished reading Bryan Peterson's
Understanding Composition Field Guide, which I thought was excellent.
I'm sure I need the composition lesson more than many other forum members, but I think even more accomplished photographers would find it beneficial. Peterson does a really good job of showing a shot, then explaining the thought process and techniques he uses to make it into an excellent image.
The topics are many of the expected ones - aperture, shutter speed, horizon lines, framing, rule of thirds - but what I found really helpful were the visual, before/after examples he often uses to make his point. It's as though he is building the composition as he is talking to you.
Even if you don't feel a need for a lesson in composition, I highly recommend this book for its gorgeous photography and very accessible style. You can get it on e-Book, but it's a very high quality paperback that's a pleasure to hold in your hands.
Here's the Amazon link:
http://www.amazon.com/s/ref=nb_sb_ss_i_2_19?url=search-alias%3Daps&field-key...po%2Caps%2C221