During the Olympics we had tickets to the boxing in the Excel center. Heeding the warnings about transport, we left 4 hours before the boxing started. Of course we had an absolutely flawless journey and pulled into the Docklands about 3 hours early!
Not wanting to just hang out in the Excel center we decided to hop on Emirates Air Line, London's new gondola transportation between Greenwich and the Docklands.
Roundtrip fares on your Oyster card (yes, you can use Oyster!) cost £6.40, which isn't that expensive, however the views aren't that spectacular. However, as the area gets built up, I'm sure this will change.