[Haskell-cafe] recommend book for self-study group

I want to encourage more people at my company to learn Haskell, but I just don't have time to prepare and deliver a class. But then it occurred to me I could lead a self-study group, where people learn on their own but would have a forum to discuss what they're learning and ask questions. I would encourage people to answer each other's questions, but I would answer the more difficult questions. What book(s) do you think would be best suited for self-study? The participants would all be experienced programmers, but would likely have no knowledge of functional programming?