The best book for me ever (so far) of U-Boats, ASW dev. and accounts of tactics and events occurring throughout the Battle of the Atlantic
(loaded with info. (tons about everything of U-Boat concerns) and very fun to read):
“In Great Waters – The Epic Story of the Battle of the Atlantic”, 
by Spencer Dunmore
While I'm at it, I just came across some nice Sub-related links:
SS-383 Virtual Tour (scroll down for many QuickTime views & great wav sound files)
www.maritime.org/tour/index.htm
Fleet Type Submarine Online – Interactive Training Manual (U.S. Fleet, WWII)
www.maritime.org/fleetsub/index.htm
Scroll down on this one and click to page number links at the "contents" - endless info. of everything!