Highly recommend the oyster card for the underground...way more convienent than trying to buy and keep track of little paper tickets anytime you wanted to ride the subway!
I just got back too... and we used the Oyster cards instead of the paper tix or the unlimited daily/3 day/ 5 day passes.
We spent 5 days in London (after I was in the English countryside for work for 2 weeks - stark difference!!) and we took it slow, for the most part. Sure, we didn't hit quite everything, but there's just SO much to do. If we tried to pack our time with an overly detailed itinerary, we might not have appreciated everything as much. Plus we were fairly low-budget so I didn't want to pay to see the inside of, say, Windsor Castle, if I hadn't seen all the free stuff yet, either.
My favorites? Probably seeing the Rosetta stone in the British Museum and watching Les Miserables (both gave me goosebumps!) in one of the West End theaters. Of course Big Ben and Parliament, Westminster Abbey, St. Paul's, Covent Garden, Tower Bridge, Tower of London, and the Shakespeare Globe were very cool too, to name just a few.
We stayed in the Canary Wharf area - which is a very new-ish, skyscraper-filled business area built over the old Quays and wharf district. It was not very touristy, but I liked it for that very reason. (At dinner, we were surrounded by business people rather than gaggles of high schoolers.) Waterfront restaurants were everywhere and other eating and shopping options were abundant. Plus, everything was clean and pretty and didn't smell bad!
The weather was pretty much perfect too.
My time in the Norfolk and Suffolk regions was very pleasant, and the people were wonderful. If you'd like any recommendations, I can pass them on.