I've only learned the slightest smattering of Haskell, in the process of teaching "Principles of Programming Languages" last spring using this textbook, whose author decided publishers were just too much trouble to deal with, and he would just put his book on the Web. It's not a Haskell textbook -- about 90% of it is in Scheme -- but he does one chapter of Haskell to demonstrate the benefits of lazy evaluation.