I went 2 years ago, I thought it was overrated (a little boring actually), and the air conditioner was broken - it was July as well.
The Imperial War Museum was brilliant though! You into history?
Try the Scottish museums, the National Museum of Scotland is a beauty, it's got loads of things, past and present.
I like London, I might end up living there depending on the job prospects for the IT sector in 4 years time.
Master of common sense. If you don't like it, stop reading.