Jeff, if you do the Hop on/Hop off Tours by either of the two big companies, they are well worth it. I would recommend it.
They have a huge number of stops in London, and in high season multiple routes, AND they sell "skip-the-line" tickets right off the bus at good prices. You can literally pull right up to Madame Tussauds, walk past the 6 deep, 3 block long line, and walk right in with the ticket you just purchased.
Well worth the price. (USD 40ish per person). Gives you transportation for 24hrs, the tickets above, other discontinued tickets and offers, and usually includes a Thames cruise with 7 stops as well.
Hope that helps. If you have any questions, let me know.