You need to visit the National History Museum, most definitely, aswell as Madame Tussaud's.
You should go to the Tower of London, that's a good trip.
If you're there for a week you should see if it's possible to see a Westend play.
And you've seen Big Ben in the skyline but you should head towards it and see it alongside the Houses of Parliament.
Man, I'm jealous. I wanna go there. :(
I do too. I've only been once. I'd love to spend a whole week in London.