Another vote for Old Lahaina Luau. Having been to several luaus in Hawaii (due to living there and having frequent guests) the OLL is the most authentic (presenting real hula from Hawaii, explaning the history of hula, etc.), decent food (really, pretty good all things considered). The entertainers are well trained and very professional. We were able to get seats (for 4) with very little advanced notice - but we were flexible on dates/times of attendance.

I've also heard very good things about the Feast at Lele.

All luaus are a bit on the pricey side - $60-$70+ - IMHO.