Doheny & Nesbitt on Baggot St. have a three rooms upstairs, two on the first floor which can be used together if the crowd is big enough. Toners across the road have a room upstairs as well. Other options are the Gingerman on Fenian Street, O'Neills on Pearse St. will cordon an area off. For something a little more upmarket, the Vaults at Connolly station have a number of rooms/areas they cordon off for groups.
Used to organise quite a few things for the social club here in work, and have used all the above, and the Russell Court. If you're bringing a large group, most of these will give you the room free, but may require a deposit. On the fingerfood, my experience is that ordering X portions for X people is never enough unless people will have eaten beforehand, i.e., not coming straight from work. If you're booking the venue well in advance, make sure you call back to ensure they still have the booking.
Enjoy,
Leo