I think most people would put the British Museum and the Tower of London on the "don't miss" list. The Tower tour will take you most of a morning and the BM will take as many days as you want to spend :-).

Borough Market is a big open air market, great place for lunch. There is a good coffee place and cheese store in the area, and the Market Porter is a great pub http://www.boroughmarket.org.uk/

For guided walking tours, I've heard good things about London Walks http://london.walks.com/ . For non-guided tours, there are any number of books at the library to help you. If you like theatre, the options are wide open.

If you like food, Jamie Oliver (of FoodTV) has a couple places in town http://www.fifteenrestaurant.com . You can find other restaurant opinions at http://www.chowhound.com/boards/intl/intl.html

The subway system (the tube) has stops all over, so do get a day pass and take advantage of it.

Bryan Oakland, CA