expedia can be fine, but they do tend to be a bit more expensive. Check their package prices against booking flights and hotels separately.
For flights - http://www.netflights.com
For hotels- http://www.hotels.com
Both have sales on at the moment so they will give you a good idea of how competitive Expedia are.

Cheers

TC

Thanks. I just compared prices for an example holiday and the results are:

expedia: £2,372.76

separately : £3,154

so expedia is winning by a long way at the moment!

Could try United Vacations, this is United Airlines holiday site for the UK. (United Airlines fly direct LHR-SFO and are ok on price) Alternatively could try Thomascook Signature who will package up for you.

I am doing a 3 stop trip in August to Hawaii (Oahu and Maui) with San Francisco on the way back. Got a quote from UnitedVacations and then ended up booking with TC Signature as they had some promo rates on better quality hotels which meant a better price than United, better hotels and breakfast included in both Hawaii hotels.
The TC signature is a good service, I dealt with the same person throughout and we spent a few days emailing and phoning to look at various options. They were happy enough to negotiate on the total price to clinch the deal.