There are many introductory Haskell books, but i was (at the time i started learning) keen of those providing also a good basis on functional programming (which was a totally new world for me at the time). ...
E. Meijer, and J. Jeuring. Advanced Functional Programming, First International Spring School on Advanced Functional Programming Techniques-Tutorial Text, page 228--266. London, UK, UK, Springer-Verlag, (1995)
J. Gibbons, and G. Jones. Proceedings of the third ACM SIGPLAN international conference on Functional programming - ICFP '98, page 273--279. New York, ACM Press, (1998)