Pick up a copy (or check the online version) of NOW magazine, it has the listings for every club in the city.
http://www.nowtoronto.com/music/listings/
Off the top of my head, more rock/metal oriented places:
The ElMocabo
The Horseshoe
Rancho Relaxo
The Opera House
Lee's Palace
If you want to see the best talent in the city, mind you, you want to check out the jazz scene, and its apex is The Rex. Every time I leave that place, I walk out with a blown mind.