The WikiBook https://en.wikibooks.org/wiki/Haskell is a good text about Haskell. It covers both elementary and advanced features of Haskell.
Real World Haskell by Bryan O'Sullivan, Don Steward, and John Goerzen
A Gentle Introduction to Haskell Version 98
The Glorious Glasgow Haskell Compilation System User's Guide, Version 7.0.1
A very nice tutorial is this one: Learn you a Haskell .
The Haskell Documentation page maintains a list of currently available books and online resources.