Tower of London is good, but expensive, good if you need a break from museum stuff. Do a tour with a beefeater, if you're really lucky you'll get a crazy furious one.
Science museum is great, natural history museum also great. V&A not a patch on those two IMO though some folks love it.
I tend to visit the british museum just about every time i'm in London, it's got a brilliant sense of place for one thing and I love the elgin marbles hall, properly monumental. Churchill War Rooms is good as is the Imperial War Museum.
Camden seems a wee bit cleaned up these days and dare I say it sanitised but the changes to the markets aren't all bad, the new extension on the stables is fab. Eat street food, people watch.
Greenwich is great for a wander around, lots to see out there and as mentioned above, take a river taxi to get there (or back, or include it in a river tour)- it's too easy to go to London and travel by underground and get no sense of how it all bolts together, seeing it from the river helps fix that.