Thanks to all of the questions/responses here on TA, I had a great trip to London. I spent 7 nights at the DoubleTree Tower of London (excellent hotel - see review). I won't go into a lot of detail, but the highlights were:
-Southwark Cathedral -went late afternoon on my arrival day after walking along the South Bank and stayed for Evensong; it's right next to the Borough Market, so you can easily combine the two
-Beefeater tour at the Tower of London
-Verger tour at Westminster Abbey - probably my favorite of the whole trip!
-Day trip to Salisbury and Stonehenge - booked a rail ticket through Megabus before I left home (very easy to do); the Stonehenge bus picks up at the train station and will drop you off in the center of town
-Victoria and Albert museum - my favorite museum/gallery of the trip - the Casting Courts were amazing!
-All Hallows by the Tower - a lesser-known church, right near the Tower of London. Be sure to visit the crypt museum to see part of the old Roman floor!
-Climbing the dome at St. Paul's Cathedral and the 90 minute guided tour (included in admission)
-Day trip to Windsor Castle
-Portobello Road Market
Overall, it was a great trip! If I could give one piece of advice to anyone planning a visit to London, it would be to not over-plan, and leave room to change your schedule. I enjoyed Westminster Abbey so much, I completely changed my afternoon plans so as to not short-change my visit. Make a "must do" list and an "if time" list ahead of time, and determine which things you really want to see and which you'd like to do if you have time. Don't rush through anything. There's so much history in London, it would be a shame to miss out on learning as much as you can about the places you visit because you're in a hurry to get to the next site.
Thanks again to all the TA members who frequent this forum - it was great to have so many experts to help plan my trip!