Lisa,
I don't know how long you'll be in London (you may have said, but I don't have a lot of time to read on the 'net these days!) - but PLEASE, if possible try to get OUT of London for at least a day or two - yes, it IS a great place, but the countryside and small towns/villages here are breathtaking, too!
Here are some sites to check out:
www.astraltravels.co.uk - I highly recommend the "Culture Vulture" tour (Castle Combe is soooooo gorgeous!!) and also the "Stonehenge Special Access" tour - the one that lets you in AFTER the tourists have gone home. I really didn't understand the big deal about Stonehenge until I went on this tour last year.
www.walks.com - this is the site for London Walks and the Jack the Ripper walk. Their pub walks are great, too, and an interesting way to meet people!
www.timeout.com/london
www.bigbus.co.uk - I really think that this company is, by far, the best to offer the "double decker bus tours" - it's a "hop-on, hop-off" service too. When I worked at the US Embassy, these buses would drive past all the time, and the guides actually looked like they enjoyed their job. They offer live commentary, whereas a lot of the other companies just have a taped commentary with headphones (kind of boring).
I don't have time to post anymore at the moment. If you want more ideas about restaurants etc etc then PM me and I'll see what I can come up with (be patient - I don't have a computer at home, so may not see any message until next week!).
HAVE A WONDERFUL TIME!
Caroline