If you don't want to head all the way in to the city I would probably go for The Narrow near Limehouse DLR. Its a nice riverside pub with a good food menu.
If you do head in to the City, there are plenty of pubs near bank station and on the back streets. I won't make a recommendation as the Fleet street area is normally where I visit city pubs.
If you like roof top bars there is Coq D'Argent on Poultry just outside bank station.
Don't go to Abacas on Cornhill.