I wrote (and sometimes maintain) two Haskell programs: funsat and bitset. Funsat is a native haskell CDCL (conflict-driven clause-learning) SAT solver. Bitset is a small library for representing sets of items using bits under the hood (as opposed to trees, which is common in functional programming).
Funsat 0.6.2 has some compatibility changes so it now works with ghc 6.12. Also, it is cabal-installable. (Before, it would die because of stupid dependencies, or something.)
Bitset 1.1 now gives you access to the Integer that is used in the underlying bit representation.