When you put "print (head p)" at then end, it keeps a reference to the
whole list "p" which is your space leak.  If you want to store the head
of p, this *should* work:

> main = do n <- getArgs >>= return . read . head
>           let p = permutations [1..n]
>           headOfP <- return (head p)
>           mapM_ (putStrLn . concatMap show) $ take 30 p
>           putStr $ "Pfannkuchen(" ++ show n ++ ") = "
>           putStrLn . show $ foldl' (flip (max . steps 0)) 0 p
>           print headOfP

The "headOfP" is computed as an IO action at that point in the program,
so "headOfP" does not hold a reference to "p" as a whole.