Disney-Kim,
I live on Oahu. I haven't eaten everywhere, but might be able to give a few suggestions.
I also like Sam Choy's Breakfast, Lunch, and Crab (this is the brew-pub that Beachbunny mentioned). HUGE portions, and great if you like surf and turf. Prepared simple.
These are on the pricey side, but very good, especially for steaks:
* Aaron's, this is on top of the Ala Moana Hotel and has a BEAUTIFUL view.
* Hy's Steakhouse, in Waikiki. Some people consider these the best steaks.
* Nick's Fishmarket, also in Waikiki. Expensive, but oh so good!!
All of the above all have live music too.
I went to the Top of Waikiki once, also a nice view, and not as expensive as I thought it would be for Waikiki.
Meritage, in Restaurant Row, is slightly gourmet, but at an excellent price. We went there for my b-day last November and I thought the entree prices were excellent for what we got.
If you want a good burger, Kua'Aina (two locations: Ward Centre, or in Haleiwa on the North Shore), is very popular and tasty.
The Shack in Hawaii Kai and Kailua also offer excellent burgers. My new favorite burger place is Eddie's on Waialae Avenue (fairly close to Waikiki), and they have this frozen custard that's out of this world!
Brew Moon in Ward Centre is also very good, and reasonably priced.
For an inexpensive but good meal, Kakaako Kitchen in Ward Centre. It's a counter service place with sit-down food. Pretty much all entrees are under $10.
For buffet, the Willows. (Shameless plug for a friend who owns the place.) Really though, it's a BEAUTIFUL setting, and the food quality and selection are very good. Dinner runs about $25, I think lunch is about $15. They usually have prime rib, a roast pig, Hawaiian food, various salads and seafood, curry, and other local items.
Get your hands on any kind of tourist magazine you see when you get here. I've heard that there are some pretty good dining coupons in them.
I could go on and on, I am such a foodie! Let me know if you know what areas of the island you'll be in, and if you're looking for more sit-down, casual, both, etc. and I can probably offer more suggestions. Feel free to PM me!