[Haskell-cafe] Functional Programming Books

[Dan Piponi]

I was just putting together my Amazon wish list and was wondering if
there are any great books on Haskell and/or functional programming
that people think are must-reads. Okasaki's "Purely Functional
Programming", Pierce's "Types and Programming Languages" are frequent
recommendations. Smullyan's "To Mock a Mockingbird" seems like it
might be a good example from the lighter end. Are there any other
classics I should know about?