We've used the Milano Inn private room on several occassions. Can't recall the cost/requirements.
We did something at Tavern on South but that has a food purchase minimum and while it's great food that might be out of our range for this type of get together.
If our house wasn't so compartmentalized (and cluttered) I'd host (downtown). But I don't really have a room other than the back patio that could comfortably seat 15-20 people. We could have 8 person "break out sessions" going at the same time in different rooms.