Ah, London, the best city in the world!
For accommodation and advice on what to do and where to go try:
http://www.londontown.com/
http://www.visitlondon.com/
I think they both offer an online booking service to make things easier.
Personal recommendation: if it's your first trip to London, definitely go on a Big Bus Tour
http://www.bigbustours.com/
It's £20 for a ticket, which you can use for the next 24 hours, you also get a free walking tour and boat trip. There are two different tours - red route (all the main attractions); blue route (main attractions plus a bit more). The red route has a live commentary, and if you get the right person these can be hilarious.
London Walks are fantastic. They do walks every day on loads of different subjects. They last about two hours but they're really not at all taxing.
With the London Pass it really depends on how much you think you'll use it. You get free entry to a lot of places on the tourist trail and transport as well. If you can get to two sites on each day, I'd say it's worth it.
London hotels are pricey. If you can find one for only £40 a night, you've done well. But make sure it's Visit Britain approved. At that price you might not be getting very much. All the ones on the Visit London site should be ok. No promises though because they are known to play fast and loose with their own rules...
I guess the main places to tick off would be St Paul's, the Tower of London, Changing of the Guard and Harrods. Plus a gallery or museum of some kind. The British Museum is really quite wonderful. You could lose yourself for days in it.
http://www.thebritishmuseum.ac.uk
That should be enough for the time being. Apart from, always used licensed black cabs. They won't fleece you and they always know where they're going.
