Light lager/blonde ale: Pine or white oak
IPA: Knotty pine (good luck with it on a lathe)
Irish red or fruit beer: Cherry
Mild/brown/Scottish ale: Walnut
Steam beer: Teak
Smooth, nitro stout: Mahogany
Imperial stout: Ebony
Spruce flavored: Sitka
Oak aged: Perhaps some oak?
Maple porter: Maple, of course!