In London, sites I would suggest are:
>> The London Aquarium http://www.visitsealife.com/london/
which is right near the London Eye
>> The British Museum http://www.britishmuseum.org/
-- full of great exhibits, including a huge Egyptian one, and like pretty much all museums in London, there is no admission fee (rather they ask for donations)
>> The Natural History Museum http://www.nhm.ac.uk/
-- very interesting and it has some great architecure, especially in the main hall (which was featured in the movie "To Sir, With Love")
>> The Tower of London http://www.hrp.org.uk/TowerOfLondon/
-- I thought it was the most interesting of the historical sites I saw there, plus you get to ride a conveyor belt as you get to see the Crown Jewels (how very Jetsons of them!)
>> Greenwich http://www.visitgreenwich.org.uk/
-- very scenic, try to take a cruise down the Thames to get there if you can (it can be pricey, but it is pretty)
>> Harvey Nichols http://www.harveynichols.com/
-- possibly to pricey to acutally buy anything, but it's worth a browse, especially the restraunt at the top)
>> Harrods http://www.harrods.com/
-- kind of kitschy decor, but a huge place definitely worth a look -- visit the pet section and the Christmas Shop, and of course the Food Hall is legendary (both are at Knightsbridge tube stop)
>> Marks & Spencer http://www.marksandspencer.com/
-- cheap & cheerful, always a fun place to look around, and a great place to pick up a cheap lunch or a snack)
>> Top Man http://www.topman.com/
-- stylish men's wear that's actually affordable
>> Next http://www.next.co.uk/
-- nice clothes, bedding & household items.
>> Camden Market http://camdenlock.net/
-- really only worth going on the weekends, a great place to wander around, you can find unique items and cheap & yummy food. Check out the store Cyberdog http://www.cyberdog.net/
(if it is still there) for the clubware (even if you wouldn't ware any of it yourself).
For bars & clubs, I really don't go out much, but I did go to:
for G-A-Y Camp Attack on Friday nights http://www.g-a-y.co.uk/?content=25&articleid=4
-- a retro night where there are separate rooms for 70s & 80's music (a huge main room), 90's (a smaller room upstairs), and the 00's (which they call "The Noughties") in a small room off the 70s-80s room. They also have a lot of live performances, although arguably (a) they are lipsynched and (b) if you're not from the UK, you may never have heard of them.
>> Ku Bar http://www.ku-bar.co.uk/
-- fun, cheap place to drink, although it is arguably a younger crowd
>> 79 CXR http://www.79cxr.net/
-- it has an...interesting ambience (and an even more interesting washroom), but it's a fun place nonetheless...and I believe all they serve are double shots for the price of a single (or at least they did when I was there!)
>> Comptons of Soho http://www.londontown.com/LondonStreets/old_compton_street_6c5.html
-- historic bar in the middle of Soho, always a great place to sit down with friends & enjoy a drink or two...or three...
Hope this helps! Have a great time! I wish I was going too!