I never see any mention of The Tower Bridge Experience. It might only get a half a star in the Big Book of must do's in London, but it's very informative, especially to those of us interested such things. The views from the top as you walk to the next tower are pretty spectacular. Another poster said the views of the bridge are great from The Tower but the reverse is also quite true.
I agree that it's well worth the experience; I actually enjoyed it more than the Tower of London visit. An enjoyable way to visit them both is by traveling there by boat from the Westminster Pier - you get the additional bonus of seeing the Houses of Parliament, St. Paul's, etc. as viewed from the middle of the Thames.