Yeah, yeah, Buckingham Palace, Tower Bridge, etc etc etc are all very good places to visit, but my favorites were some lesser known attractions.
London Transport Museum-I think it's in the Covent Garden area,
River Thames Flood Barrier-a few miles east of Greenwich.
A boat tour on the Thames-Try to time it at low tide. It passes an area where lesser criminals who didn't deserve execution by beheading were chained to the bulkhead at low tide and the rising river finished the job.
Jack the Ripper tour
A Tower of London remembrance-we visited six weeks after Princess Diana died. There was absolutely nothing about her at the Tower. All traces had vanished. Almost every gift shop elsewhere, and even shops that normally didn't sell tourist tchotchkes, had plenty of Diana memorabilia. Further proof that the Royal Family was behind her death???
Oh, and the Tower gift shop individually scanned every single item, when such a practice wasn't yet widespread. Even postcards, magnets, keychains, and other cheap crap. I guess Liz wanted to know exactly how many postcards of Princess Margaret were sold.