Please chip in with further ideas
Travel to London
London has 5 airports; direct flights from SFO go to Heathrow. Currently BA, Virgin and United fly direct. Gatwick Airport also has flights from the US - mainly East Coast. (BTW if you are thinking of redeeming miles, you might need to try routing via LA as award availability is usually better.)
To get from Heathrow into London, take the Piccadilly Line (40 mins, underground) or Heathrow Express (15 mins, overground). Piccadilly line is much cheaper and is covered by Travelcard (see next).
Travel within London
Public transport is comprehensive and fairly reliable. 'Travelcards' cover all tubes, buses and some overland rail. Available for 1 or 7 days, these can be bought from any tube station. (Many convienience stores also sell them.) Example; £25.80 7 days for central zones 1 & 2.
London transport site: http://www.tfl.gov.uk/
Travelcard pricing: http://visitorshop.tfl.gov.uk/english/travelcards/product/Anytime-7-Day-Travelcard.htm
Tube map: http://www.tfl.gov.uk/assets/downloads/standard-tube-map.pdf
Don't hire a car - parking is limited and expensive. And we drive on the correct side of the road...
Strongly recommend staying in Central London. There will be very little to do at Wembley when the game is not on, and frankly, it's not a great suburb. Since it's not hard to find an expensive hotel on Expedia or Kayak, I'll only paste links for a couple of the budget chains - both have multiple sites in London.
Getting to Wembley
Get the tube to Wembley Park - served by Jubilee and Metropolitan Lines. Alternatively, take overland train from Marylebone to Wembley Stadium. Wembley is in Zone 4.
Eating / drinking
I'll add to this later...
If you want to take in some football / soccer, Chelsea, Arsenal, Tottenham, Fulham and West Ham are all in the Premier League. Fixture lists for the 10/11 season will be published in June. Tickets are typically £40-£50 but can be hard to get.
Other stuff in London
A couple of tips here rather than a full list;
Museums: Strongly recommend The Cabinet War rooms if you're into history - Churchill ran WWII from here. Located on Horseguards Parade by St James' Park. The Natural History Museum and Science Museum are both good - next to each other in South Kensington. The British Museum is full of stuff we, erm, 'borrowed' from other parts of the world. (Like Athens. And ancient Egypt.)
Art: The National Gallery and National Portrait Gallery are both free and next to each other on Trafalgar Square. Tate Modern on the Southbank is also worth a visit.
Southbank: The south side of the River Thames between Westminster and Tower bridge is a long strip with loads of restuarants, bars, Shakespeares Globe, Tate Modern, museums etc etc. Very good for wandering.
Oxford and Cambridge are easy day trips - about an hour by train. Windsor is about 30 minutes - all are good for a bit of history and 'Britishness'.
Don't bother with Stonehenge - it's a few rocks in a field. Waste of time.
Paris and Brussels are both about 2 hours on the train. www.eurostar.com
[ Edited by London9er on Feb 2, 2010 at 10:00 AM ]