I have read "The Craft of Functional Programming" by Simon Thompson and a few paper on the web. "The Craft" is a good book, but it is an introduction to FP. It seems to me it there are a lot of books on OO design I can pick up at the bookstore, but in the FP world, one must worm their way through all sorts of papers. I have seen papers on Catamorphisms, Monads, Programming with Barbed Wire, folds, etc. I think these papers are hard to understand if you don't have the acadademic/mathematical background -- being papers and not textbooks these papers assume a fair bit of base knowledge.
I agree with this completely. The CFP book is a good introduction. Unforunately, the " Gentle Introduction To Haskell" that haskell.org links to is not a very useful introduction. I am getting more out of Rex Paige's Two Dozen Short Lessons in Haskell. ( I am studying Haskell and C# on my own in my spare time as break from my medical practice ).