Keep it in the vicinity of the city would be the best bet I'd reckon. In the last couple years I have been to 21sts at Griffins Head, Caledonian, Colonel Light (great space upstairs, not sure if they still hire it out), Kentish Arms, British Hotel, Alma (upstairs), Cowandilla Sports Assoc, Cathedral, OXford, WAFC, Southern Parklands convention place (cant remember what its called), The Stag (upstairs), Maid and Magpie, Payneham Tavern (booked out whole bar area but had a few scragglers in who wanted to use TAB).
Best ones were probably (taking into account you want room for 150 or so) would be Colonel Light, Griffins Head, Payneham Tavern, Alma, Kentish Arms, British Hotel, Catherdal in that order.