Go to Emirates Fly in Greenwich for a balade on air over the O2. It's something to not miss. If you're going for the first time, then go during the day, you'll appreciate the view more, if not, then take a ride at night, It's different.
Go to Camden Town, It's a nice "get out of routine" place/market; taste the food and enjoy the crowd.
Ps: There're a loot to do in London beside the parks and the palace