Welcome Joyce! As Liz said, detached houses in London proper will be harder to find, and very, very expensive. Areas that I know other American expats live, and have detached houses with small gardens (back yards), albeit hugely expensive, are Fulham, Hammersmith, Wimbledon, and Richmond (all part of Greater London, I believe.) In Kensington and Chelsea (a bit closer to central London) houses are even more extraordinarily expensive and hard to find (detached houses, that is.)
We don't live in London, but in a small village in Surrey county - about 30 minutes by train from London Waterloo station (central London.) Surrey is the county just SW of Greater London. Hampshire is a bit farther out from London - it's west of Surrey. TONS of people live in our area and commute to London daily - it doesn't seem to be that big of a deal. In fact, I can be in central London just as fast from out here (Surrey) via the train as some friends who live in Wimbledon coming in via the Tube. We chose this area because my husband's company is located in Surrey (Guildford.) I think it's a great area - close to the city (London,) yet a bit more rural and relaxed. Our village is lovely - looks like a traditional "English village" - several very old pubs on the High Street, lovely green where the local team plays cricket in the summer, quaint old church, nice people. Kind of the best of both worlds, IMO.
One site that was helpful when we were exploring where to live last year was
http://www.findaproperty.com/You can search by all sorts of different criteria on that site - I found it very good.
I agree with the other posters about large SUVs - you don't see as many as in the States! You will see some, but many of the streets and roads are very, very narrow. Parking spaces are much smaller and narrower, too, and parking ramps have much less room to manuver. I had a Jeep Grand Cherokee in the States and am very happy with my little VW Bora here.
Is the company having a relocation consultant work with you? They can be very helpful - several people I know have worked with relocation consultants and were very glad they did - saves you from having to do so much of the work, and there is a huge amount of work in planning an international relocation. I know - we had to do most of it ourselves last year!
Another good resource is a book published by the Jr. League of London called Living in London
http://www.jll.org.uk/UserArea/StaticPages/LivingInLondon.aspLots of useful information about Living in London and the UK. I have found my copy indispensible!
Good luck! You'll have a much better feel for things once you get over here and can actually LOOK at different houses, areas, etc. It's an exciting opportunity to live in the UK! We've been here for a year (one year tomorrow!) now with a job-related move, and are settled in and really enjoying our life here.
Stephanie