Haskell.org- the page for the organization overseeing the development of the haskell language has many online resources and information.
Hugs98 web page- The web page for a free Haskell98 interpreter.
http://www.numeric-quest.com/haskell/hcompanion/
The Haskell Comanion- a great site with scads of information re: Haskell, and functional programming in general.
http://www.cs.utexas.edu/users/ham/UTCS/CS307/
Online notes and assignments for a first year CS course from UTexas at Austin.