We got married last September and had a 2 week honeymoon in the states.
We booked with Virgin Holidays and they were great at sorting out flights, transfers and hotel changes etc.
We started with 3 nights in Vegas, followed by 7 nights on Oahu Hawaii, ending with 4 nights in San Francisco (flying from Gatwick). (We'd got engaged in Vegas, and were keen to go back on our Honeymoon. Incidently, we're heading back there for our first anniv).
We stayed at the Palazzo in Vegas, and knowing what to expect from Vegas we had a cracking mad start to the Honeymoon. Plenty of drinking, eating over indulgent American portitions of food, and a bit of gambling. I think it's been mentioned on this thread already about what to expect from Vegas, but it's like a giant adult playground, and if you like a laugh and don't take it all to seriously it can be incredibly fun. One tip for Vegas is to head down to Freemont Street at night for the lights show.
On Oahu we stayed at the Kahala. It's a fantastic hotel on it's own just up the coast from Waikiki so that you can avoid the hussle and bustle when you want to. It's a very romantic place and perfect for a Honeymoon. We hired a car whilst there and drove around the island. I loved where we stayed on Oahu and also enjoyed all of what Waikiki had to offer but for pure beauty you couldn't beat the quiet beaches on the east coast and north of the island. We also found a Botanic garden on the east coast whilst driving around that had a natural waterfall lagoon that you could swim in. It doesn't get much more romantic than that!
We stayed at the Fairmont in San Francisco, right at the top of Nob Hill. It was my first time there and I loved it. To be honest, given the choice again we may have chosen a different hotel. As although the Fairmont was very grand, it was also a bit impersonal. I far prefered the more informal hotels closer to Fishermans Wharf, where you didn't have the hill trek back to the hotel everytime you went anywhere. San Francisco is a fantastic place and I was surprised by how european it felt compared to the rest of America. There are some fantastic breweries there and plenty of bars to drink the beer in.
If you do end up there, definitely do one of the bus tours around the city and over the Golden Gate bridge, and Alcatraz at night is fantastic. You can buy the tickets quite cheapily on the net before you go.