The last time I was in Oahu, I was with some friends who have been there several times. Here are some suggestions:
1. Eggs n Things on Kalakaua Ave. Best breakfasts ever! Huge portions. Try the coconut syrup on your pancakes. Yum!
2. Golden Dragon Restaurant in the Hilton Hawaiian Village. Best Chinese food I've ever had. Also, huge portions. Really nice.
3. Cheeseburger in Paradise - also Kalakaua Ave. Music in the background, prices not too bad, and we got in without a wait.
4. Dukes - in the Outrigger on the Beach - Kalakaua Ave, food is good, music in the evenings, make reservations!
5. Shorebird - in the other Outrigger (Reef). I didn't go that night, but everyone seemed to like it.
6. Tiki's - I haven't been there yet, but my friend the Big Kahuna tells me they're good. I plan to go when I'm there in Oct. It's in the Resort Quest Waikiki Beach on Kalakaua Ave.
7. If you get a chance to go to the North Shore, and you go to Haliewa, make sure to go to Matsumoto's for shave ice. Get it with a scoop of ice cream in the bottom, and adzuki beans, then the shave ice. It's the best!
Have a great trip! Hope this helps.