Daly's Seafin Teak Oil. It is what Hunter used originally on the interior, and available from West Marine. It's extremly easy to apply and one good coat will last 2 seasons or more. If you want to really (REALLY) make things look nice, after a couple coats of Seafin, apply 3-4 coats of Daly's Profin Gloss, lightly sanding with 800 grit before the final coat. Application is VERY easy, just wipe on and let dry!
It's not a very good pic, but I snapped this from my phone last night while at the boat, you can see what a few coats of Daly's Profin Gloss looks like over top of a couple coats of the Seafin Teak Oil. I have done almost the entire interior woodwork at this point and it looks fantastic.