If you're visiting the O2, you'll be around Greenwich. A couple of regular boozers for me in that neck of the woods are:
The Gypsy Moth - this is by the Cutty Sark. If you arrive in Greenwich via. the Thames Clipper, it's the first pub you encounter. Good food in this one, a lovely little beer garden. They used to have an unusual beer selection, but someone bought it out a couple of years ago....I think Taylor Walker or M&B.
The Greenwich Union - A meantime pub, and Meantime make a lovely pint. If you're a real ale purist, maybe not for you as Meantime have adopted the American style 'pale ale' revolution everyone is going mad for - so it's all Nitro tap. If you're more up for a traditional pint head next door to
Richard I - Probably the best beer in this area. Had a couple of sessions here.