You'll need to provide a bit more information, so people can help you. Such as: Where are you staying? When? What kinds of activities do you like doing, other than beach time? Will you have a car? How many in your party? Any kids? How old? What is your budget for activities? Restaurants? Alcohol? Any mobility issues? You get the idea.

Dave
I agree. Also, is it your first time to Oahu or any of the Hawaiian Islands?
Here are some ideas based on places we've taken family/friends when they stay with us.
Pearl Harbor
- U S S Arizona Memorial
- USS Battleship Missouri Memorial
- Pacific Aviation Museum (optional, if you have time while you're at Pearl)
National Memorial Cemetery of the Pacific (aka Punchbowl)
Gardens
- Foster Botanical Gardens
- Lyon Arboretum
- Ho'omaluhia Botanical Gardens
Shopping
- Aloha Stadium Flea Market
- Ala Moana Shopping Center
- Hilo Hattie Flagship Store
- Various Farmer's Markets -
http://hfbf.org/markets/
Island Touring by car
- Dole Plantation
- Byodo-in Temple
- Laniakea Beach (aka Turtle Beach)
- Beaches such as Lanikai Beach -
http://www.hawaiigaga.com/oahu-beaches.aspx
- North Shore
- Shrimp Trucks
- Matsumoto Shave Ice
Sunday brunch (very nice but pricey buffets)
- Orchids restaurant @ Halekulani Resort
- Hoku's restaurant @ Kahala Resort
Iolani Palace
Bishop Museum
Doris Duke's Shangri La
Complimentary Cultural Events at the Royal Hawaiian Center
Polynesian Cultural Center
Waikiki Aquarium
Diamond Head
Snorkeling at Hanauma Bay Nature Preserve
Walk along the main shopping strip in Waikiki (from the Marriott (near the Zoo) to Fort Derussy (near the Hilton)).
Walk along the waikiki beach area
Special Interest: Music (my nephew is active in the school marching band and jazz band)
- Ukulele Lesson at the Royal Hawaiian
- Ukulele Factory Tour (10:30am)
- Royal Hawaiian Band
Special Interest: Art Museums (my mother in-law loves Museums and so do I)
Honolulu Academy of Arts
The Contemporary Museum