Tower of London - We were there when it opened and went straight to the crown jewels treasury. We were the only two in that building and they had not turned on the moving sidewalk yet so you could really get a good look. (no photos allowed inside treasury). Lots to photograph outside & other buildings in the Tower.
Boat Ride down the Thames to Greenwich. Tour observatory and ride back. (half a day)
Grey Line has an all day tour to Windsor Castle and Hampton Court Palace.
Grey Line also has a half day tour to Leeds Castle. Very photogenic!
I need to upload some photos to post for you.
Bob & Nan