"Another Place, Another Time: A U-boat Officer's Wartime Album" is a very good book. Lots of interesting photos, particularly the detailed tour of a Type IXC/40 appendix. Available here:
http://www.amazon.com/Another-Place-.../dp/1591140137. Overall 5 star rating...
I'm reading "Hitler's Grey Wolves: U-Boats in the Indian Ocean" at present. It's an interesting book as well. Here is a good review of this book at Stone & Stone:
http://stonebooks.com/archives/050213.shtml to help you decide.