hey, definititely go to Buckingham palace, the tower of london, Trafalger quare, the London eye, you can take a boat rige down the Thames that is quite nice. The tube (underground train) is fairly easy to get round on, just watch your camera closely! Also you can do on one of those tourist open top buses and see most of the city. There is so much to see in London, great city!
have a great trip!