Where are you staying? I think Oahu is the most versatile place for a holiday. Bit of everything, great weather, it's easy, clean, safe etc. Waikiki sometimes gets a bad wrap as its very touristy but it works so well. Plenty of things to see and wander around, go shopping and eat on the main stretch. ABC stores carry everything you'll need and they are everywhere.
15 minutes away and you are in a different world. Beautiful country, friendly locals with reasonable prices.
It's really worth paying the money for a Pearl Harbour full day tour. The local guides are excellent. The yanks do this stuff really well.
-Haiku Stairs isn't a bad walk.
-Diamond Head was OK but i certainly wouldn't pay for the tour.
-The zoo and army museum are ok for a short look if you are into that. Both a bit basic but we all need to support these things.
- Take your wife swimming with the dolphins. Major brownie points

- Kaluia Ranch. With its movie location tours etc it can be a bit touristy but the fact is its still one of the most beautiful places on earth.
- North Shore, nuff said!! You'll want a car for this. Can be done by tour or bus but it'll take longer.
Heaps of walks, beaches and bays to stop at as well as other touristy stuff you'll see on the brochures. You can't really go wrong anywhere in Hawaii