Haskell Reference at Zvon
A thoroughly indexed reference to Haskell syntax and libraries with many examples. http://zvon.org/other/haskell/Outputglobal/index.html
Haskell: The Craft of Functional Programming
By Simon Thompson; Addison-Wesley, 1999, ISBN 0201342758. Edition 2, introductory textbook to functional programming in Haskell. [University of Kent] http://www.cs.kent.ac.uk/people/staff/sjt/craft2e/
Haskell Tutorial
An introduction to Haskell, including explanation of basic concepts and exercises. [Postcript] http://www.di.uminho.pt/afp98/PAPERS/Tutorial.ps
Online Bibliography of Haskell Research
Provides a constantly-growing bibliography of papers, and theses, on research related to the Haskell programming language. Links to online copies of each paper are provided, where available. http://haskell.readscheme.org/