The Fox at Connaught (out at the east side of the centre) is alright, though generally better if someone else is picking up the bar tab. They normally have some ales on, and mediocre food.
If it's a nice day, take the
dangleway over the river from near the west entrance to Excel, then it's a short stroll to the Pilot Inn, a rather jolly little Fuller's pub on the Greenwich Peninsula. Note that the cable car stops running at 2100, so you may need to get the Jubilee Line + DLR back again.
Alternatively, you could try some places on the official
DLR Ale Trail.