Possibly parallel and memoised fibonacci.

gistfile1.hs

import Control.Parallel

nfib :: Int -> Int
nfib = (map fib [0 ..] !!)
   where fib 0 = 0
         fib 1 = 1
         fib n = par n1 (pseq n2 (n1 + n2))
            where n2 = nfib (n-2)
                  n1 = nfib (n-1)