Rent a car on Oahu. You can see the island much better with a car even if it is just 2-3 days.

You won't save any $$ by not renting a car.

While I agree with dusty that you can see the island better with a car than without, if you really just intend to stay in Waikiki and maybe go to Pearl Harbor, the answer is no, you don't need a car. (But the rest of the island is worth visiting, even if you just do a day trip around the island)

A direct answer to your question would be no you don't need a car but as sf and Dusty both said you would be missing alot.
The drive around Diamond Head to Makapuu and up the windward side around to Kaena Point is as scenic a drive as anywhere and the view from Nuuanu Pali Lookout.

If I had just 2-3 days on Oahu I would want to spend most of my time on the beach, with a wee bit of shopping. I would not want to spend it in a car! Don't get me wrong...I love Oahu and usually stay on the windward or north side of the island where a car is a "must". Sometimes I stay in Waikiki for a couple of nights and I never rent a car. Hotels charge a fortune for parking, and many of the hotel garages are a block or two away from the lodging. Taxis are plentiful and it's easy to hop a bus to Ala Moana or Chinatown. You would probably get a tour package for Pearl Harbor that would include pick up at the hotel (arrange through concierge).
I vote a big "no" on car for the trip you have described.

You can "get by" without a car, but I love driving around Oahu and would not be without a car there unless I were down and out.

I would rent a car. We were there last March for a week and were so glad to have a car. Getting to Hanauma Bay or elsewhere to snorkel, or Diamond Head, or Pearl Harbor...all of those are much easier with a car. I would take the suggestion or driving around the island as well. We loved Waikiki, but the rest of the island was so different and we were glad to experience that as well. Loved it all!

I agree, it's possible if you are just going to veg out, but it's preferable, in my mind, to rent a car. Friends of ours were actually stood up by their shuttle service to Hanauma, thus knocking them out of that wonderful opportunity!

Loved the circle island tour - I've misplaced the link, but if you're interested, I'm sure Dusty will provide it.

Thanks for all the responses. We will take them into consideration - still trying to decide! I just looked up the parking and rental car cost today and it's so expensive!!!

If you are staying near the Hale Koa, you can park there for about $12 per day. Guest of that hotel pay less, but the general public can also park there. It is a military hotel, so many people think their parking garage is off limits to others, but that is not the case, and it is about half the cost of other parking in the area.

We spent 6 days in Oahu. We spent most of the time relaxing at the beach or at the pool. We also walked around Waikiki, especially at night - which was great fun with all the entertainment. We decided to rent a car for the day (booked it through one of the car rental places on Kalakaua Ave. as it was much cheaper than renting throught the hotel concierge) and took a ride to the North Shore. I just loved it, especially the Farrington Road beaches. I think they were the nicest beaches we saw on Oahu and Maui! We returned the car after our trip and never had to pay for hotel parking.

It depends on what types of things you want to do. If you really won't be venturing away from Waikiki that much, I think it's convenient not to have a car. Another option, which is what I usually do, is to rent a car for 1-1.5 days. Several of the agencies have offices in Waikiki (Hertz, Budget, possibly others)and it's easy to pick it up right there. That way you could decide to go farther afield without the expense of parking the car for multiple nights at the hotel etc.

I've been thinking that I want to rent a car on Oahu for just my last two days (or maybe three) of a week there. I thought I'd pick it up in town and drop off at the airport when I fly off to Kauai. But it seems everyone is charging $25 extra to drop off at the airport when you pick it up in town. If I have a bus pass, which I probably will, I guess it makes sense just to take the bus to the airport and pick up my car for driving around. (No luggage involved going to pick up the car.)

Does that make sense?

There are a couple of driving tours on this thread.

http://www.fodors.com/community/united-states/first-trip-to-hi.cfm

You can also drive to National Cemetery of the Pacific & Tantalus Drive just above the cemetery.

Do we need to rent a car in Oahu? No!

Is it an advantage to rent a car on Oahu? Yes !

is it cost effective to rent a car on Oahu? Maybe. It depends on what you want to do.

Ignore what I said above about the drop off charges when picking up downtown Honolulu but returning to the airport. I just booked National, which has the best location for me, just two short blocks from the condo I'm renting. I did it through Costco, and got a car for two days dropping off at the airport for a total of $$62 -- that was $26 a day before the taxes and fees. I wasn't finding anything for under $90 or more on carrentals. com and all the others (and Hotwire/Priceline doesn't let you do the one way rentals or choose your pick up location).

I stay in the Waikiki area and do OK without a car. I take a taxi to and from the airport. Then get around mostly on foot and sometimes using The Bus. With just a couple days for the things you say you want to do, I don't think you need one.

I think we are going to stay at Waikiki Marriott. Is that a good location to be without a car for 2 days? Anyone knows if there is a Budget rental station in that area?
We have 3.5 days in HNL, arriving Friday late afternoon and our flight departs 11 pm on Monday. I like the idea of renting a car for 1 day to do a driving tour and go to farther areas. The rest of the time we plan to relax, walk around waikiki beach, we do want to visit Pearl Harbour and possibly China Town...maybe even do a bit of shopping.

Sayko, I agree with those who mentioned renting a car for a least a day(or part of a day)and you wouldn't have to decide until you arrive as there wouldn't be much of a benefit to booking the car ahead of time. Waimanalo Bay beach, Lanikai Beach and Hanuama Bay (for snorkeling) are amazing and not too far from Waikiki. You will still get your relaxing in on these beaches and they are far less crowded than Waikiki.
I guess it depends on your personality and if you like the busy atmosphere of Waikiki. BTW, I stayed at the Marriott in '07 and thought it was a great location.

Yes, the Budget rental location is in the Hyatt, which is not far from the Marriott

"I think we are going to stay at Waikiki Marriott. Is that a good location to be without a car for 2 days?"

You can park at Aston Waikiki Banyan for $10/day. It is close to Waikiki Marriott.

Without a car, you would have to pay for shuttles, cabs, buses, so you won't save much if any by not renting a car.

Get out & see Oahu with a car.

My first two trips to Oahu were without a car. My last four have been WITH a car. I prefer having the car.

But with the things you said you want to do, you really don't have to have one. I visited the Marriott last September and have decided that I might try to stay there on my next trip this September. There is cheaper parking very close by, as someone has already mentioned.

You can buy a day-pass on the trolley, which will take you to shopping as well as to Hanauma Bay for snorkeling. It's one of those hop on/hop off kind of shuttles, with the driver telling you about the sights along the way.

There is plenty to do in and around the Marriott. A nice section of beach is directly across the street from the hotel; but the pool on second floor is also nice!

Have a nice time.