The Senate needed to be convened by a magistrate, and could meet in any inaugurated space (templum); and was preceded by a sacrifice and the taking of the auspices. (according to Gellius 14.7)
In addition to those mentioned by "Novosedoff", meetings were held in the temple of Fides (before the killing of Tiberius Gracchus) and in the temple of Tellus.
There was also a curia associated with Pompey's Theater complex in the Campus Martius. The meeting at which Caesar was assassinated was apparently held there.