Nike trains M, T, Th, and Saturday. In the summer/spring/fall they train on Wednesdays at the east river track, but they stop that post marathon.
Mondays start at 6:30 out of Time Warner Center, T, Th, Saturday from NikeTown. Groups are large and unregulated, so you can generally find someone running at your level. All Nike runs are free.
CPTC has a pretty hard core running group -- you can check out their runs on their website. Their group are sub 34 10k, 34-38, and 38-42, so there should be a group for you there. Dues are 125/yr.
Warrent Street does a Tuesday night in CP and a saturday/sunday run. They seem semi-hardcore, but haven't recruited a bunch of "ringers" like some of the other clubs. And their runs are free.
You already have a coach, so John Henwood probably doesn't make sense. But he runs some speed workouts as well.
I think the harriers run on the east river track on Wednesday nights as well. I don't know much about them.
Hope this helps.