Haskell is yet another functional programming language.
Haskell together with Clean are two unique programming languages in sense they are both completely strict functional, still allowing writing of interactive programs. That is they always maintain referential transparancy.
Also, both of Haskell and Clean are very strict typed languages (sure, what would be fun of being strict functional without at least minor ability to prove program properties?). Both of the type systems are based on variations on Hindley-Milner types. Both of the languages are defined lazy (and thus permit very nifty operations on infinite data as long as some very simple but head-smashing concepts).
Haskell has very elegant and powerful degree of polymorphysm, type classes (wich have nothing to do with OO-classes, though type classes do permit OO-style programming in haskell to some degree). It is even powerful enough to define monads, which are Haskell's way of interacting with outer world.
Haskell has a very good central site, which it a really superb source of links, documentation (including tutorials and language definitions), code and tools for haskell -- http://www.haskell.org
Here, on the InteLib page, Haskell-related work is leaded by MeDendik in HaskellFiles project.