The river cruise from Westminster to Tower bridge was a great trip. We got there and there was absolutely no line at all. We got our tickets and only waited a matter of 10 minutes before getting on the boat.
I highly recommend the top deck of the boat. You get a way better view and the sun shine.
There was a tour guide on this trip but he was not your average tour guide, he was a lot of fun and made the trip interesting. He told occasional jokes which made the journey more fun. Close to the end, the captain was so kind to turn the boat at a great angle so that us (the passengers) could get a really fantastic picture of Tower Bridge. I highly recommend this trip for all ages.
Tourists especially, you get a look of London from something other than a bus of train. Great prices too.