Well, if you're visitng O'ahu island:
There's skydiving and plane rides at Dillingham Airfield if you're a thrill seeker http://www.soarhawaii.com/
There's the Wet and Wild water park, but I don't know if it's up to snuff with the one on the continent. Ko'olina beach and resort is a wonderful place to kick back and relax. They've got four lagoons, some really nice hotels (the new Disney Hotel is up too).
There's the walk up to the Makapu'u Lighthouse. It's got a great view of the ocean, and I loved the hike up. http://www.hawaiiweb.com/oahu/hiking_and_camping/makapuu_lighthouse.htm
If you want shopping, I'd also suggest Ala Moana and Waikiki. Other great places are Pearlridge Shopping Center, and the Waikele Outlets.
Haleiwa Town is a great place. You've got the beach close by, then you can walk over to Matsumoto's or Aoki's for some great Shave Ice. I reccommend getting Azuki Beans and ice cream along with it
If you're going for some anime good, I suggest Toys N Joys. http://toysnjoys.com/
Well, I hope you can come for a visit to our wonderful island home, and if you do, I hope you have great time here.