This weekend it's the Thames Festival!
There are events up and down the length of the river all weekend, from music and spectacle, to river races, Thames barges, kayaking, and fireworks.
I almost forgot all about it, even though put a note in my calender. Alas too busy to do anything but spectate the Great River Race, but if you are in London its worth poping down to the river bank in the centre of town to see what's going on.