Can I just ay one word - JEALOUS!!!!
I love London, and hope I can go back again soon!
One of things I utilized when I was studying in Cambridge (went into London fairly often) was a tour bus company called "The Big Bus Company" (
http://www.bigbus.co.uk/) It's a hop on/hop off tour that takes you to the "main tourist" spots, and it was a great way to get around the city as well (though I enjoyed riding the Tube, too
)
Enjoy your trip over there!