Haskell: Your 2005 Programming Language

I really enjoy the book The Pragmatic Programmer. One of the suggestions in this book is to learn one new programming language every year. Since the new year is upon us, I though I'd suggest that this year, everyone should learn Haskell.
So please apt-get install hugs, grab Yet Another Haskell Tutorial, and get hacking. You'll probably want to have the Libraries API bookmarked. You might want to install the Glasgow Haskell Compiler after a couple of hours.
When you get ready to package your first Haskell library for Debian, be sure to check out the state of the Haskell Cabal (the Common Architecture for Building Applications and Libraries).
Here's a basic implementation of cat in Haskell. Compile With: ghc Cat.hs -o myCat

import System

main = do a <- getArgs
          contents <- sequence (map readFile a)
          putStrLn (concat contents)

I'd be very happy if folks email me with suggestions on what programming language, API, technique, paradigm, or whatever I should learn this year. You definitely get extra points if you can give me a link to a good tutorial and if an implementation of the language is packaged for Debian.