I've had great results with real boiled linseed oil. I've done it where it's brushed on fairly heavy, then after a couple of days, wipe it off to fill the pores. Let it dry for a couple more days then top with Permalyn or Chambers finish. Or, just lighter coats of real boiled linseed oil. I love the look...
But, if you don't want to go that route, like Mitch said, spar varnish works really well also.
Ed