Please, please, please don't make Oahu as the main destination for your once in a lifetime trip. Just a suggestion.
We lived in Hawaii for 3.5 years, on Oahu. I always felt SO bad for people who saved up for years, to make this "once in a lifetime" trip, and then spent the whole time on the most crowded and congested island.
We visited Kauai for our 1 yr. anniversary and it was absolutely WONDERFUL!!! It's everything that you expect Hawaii to be.... I've heard Maui and the big island are the same way. Not to say that Oahu is a dump, LOL, but it's..... just...... let's just say it's not like that idea that you have in your head that Hawaii will "be like". It's definitely worth visiting; Waikiki, Diamond Head, the North Shore, Ko Olina, Pearl Harbor, etc. are all nice places.... but it's not awe-inspiring paradise either. I only felt that way about Kauai....
Just my personal opinions, no flames please
I have agree with this. We spent a week on Oahu for my DD's Make-A-Wish trip. It was not all all what I expected. Don't get me wrong, we had a great time but the only place that we had "this is the most beautiful place in the world" thought was looking down on Hanauma Bay. Besides that, it was like a "little Chicago" on the ocean instead of Lake Michigan. We did enjoy the few hours we were able to snorkel, see the sea turtles on the North Shore and seeing Pearl Harbor was a huge hit for DH and my older DD. It just wasn't the relaxing beautiful paradise that you think of when you hear
Hawaii.
MAW did offer for us to see more than 1 island but the logistics of it, just didn't work out. We would still have only had 5 days there (plus the day we got there and the day we left) so we would have wasted one packing, checking out of the hotel, returning the rental van, sitting at the airport, getting the new rental van and checking back in at a hotel. There was also a lot of specialized stuff that we needed for DD.
If I had it to do over, I would have asked if we could have extended our stay at our own expense so that we could have seen both.
Thanks for all the great ideas! Please keep them coming! We are in Illinois if that helps. The beach is a must, history and culture not so much. Just natural beauty, what you think of when you think of Hawaii...
Kauai and/or Big Island.
I'm leaning towards a 10-14 day trip to accomodate both islands.
We're also thinking of beginning or ending in Oahu so we can do Pearl Harbor, etc.
I"ve had many people tell me just to go to the Caribbean...flying from the midwest [Indiana here], you lose about 2 days flying. So part of me wonders if there's any truth to that. We have traveled to several Caribbean islands and the Mayan Riviera [my fave for affordable and easy to get to and around].
Trish
We're from IL. I will tell you that we had a horrible time adjusting our body clocks when we got back. The non-stop flight was just under 8 hours but there's also a 5 hour time difference. We left HI at 4 in the afternoon and landed at O'Hare at 5 am.

I'm not kidding when I say that it took me over a week to where I was feeling normal again. I just couldn't get over loosing an entire night of sleep.
We had no problem adjusting when we were in HI. We left Chicago around 9 am and had a quick lay over in San Francisco landing in HI around 3 (which was 8pm our time). We ended up staying up to about 10pm (3am) but had no problem getting up.
As for budget, MAW planned and paid for our trip but we did get a breakdown. The flights were a little over $1,000 each, the dolphin encounter for DD was $500, the luau was $107 a person, the rental car was just under $400, parking at the hotel was $33/night, Pearl Harbor and the boat ride to the Arizona Memorial is free but we did pay $20 each for DH and the 2 older girls to take the tour of the MO. (I stayed at Pearl Harbor with DD as they said it would be difficult to get her wheelchair around). MAW gave us $2850 to spend while there for everything else (food, drinks, gas, tips, baggage fees...) I was afraid that it wasn't going to be enough money but it was. We actually ended up having about $1,000 left but we didn't eat at
fancy restaurants. Most of the meals ended up being around $100 for a family of 5 so it wasn't too bad. We stayed at the Hyatt on Waikiki Beach. I'm not sure what the room charges were (they gave us 2 rooms) because it was all taken care of my MAW. Gas wasn't much more than it is here. I think that it was about $3.25 and at the time it was about $2.90 here.
Have a great time!