Oahu is do-able without a car. If you stay in or near Waikiki you can have the beach, shopping, dining, etc. easily available. In fact, in Waikiki a car is a problem due to limited and expensive parking. I'd suggest renting a car for only a day or two on Oahu to explore the north shore and other far reaches of the island. The best beach, IMHO, on Oahu is to be found at Kauai Beach Park. It is also possible to reach all of Oahu on the bus - so you can get by entirely without a car.

All of the other islands have wonderful things to offer. And, on all of them, you'll pretty much need a car. I'd suggest looking into some of the interisland travel packages which include interisland airfare, car rental, and hotel. The rates are often better than you'd get booking the pieces seperately. I think, roughly, that of three islands you mention - Maui probably has the 'best' beaches, Kauai has the most breathtaking scenery, and BI has Volcano National Park - there are strong arguments in favor of any of the three islands. If you want to avoid driving, though, I'd recommend staying on Maui in or near Lahaina. (You'll still need to find a way from the airport to Lahaina - and you won't be able to see the island without a car.)

I can't recommend any specific condos - I live here and I just don't know what is available.