Eric's Seafood Grotto - great seafood, great prices, nice wait staff - be sure to sign the guest book.
Mama's Fish House - little pricey, but the ambiance is worth it!
The Road to Hanna - fun to do yourself, make sure to go to the Seven Pools for a dive. Takes all day. If its not the rainy season - you can travel all the way around the island (even though the car rental companies don't want you to).
Hawaii on a Budget dot com - great place to get reduced prices on things to do.
There are a couple good snorkel outfitters - make sure you do your homework on those.
Have fun - its one of the better islands!!
ALOHA