If you get the chance, you should go down to the notorious Air Canada Centre where the Toronto Maple Leafs play NHL hockey. I'm a huge hockey myself, so I can appreciate the "aura" of the old building. :)
The Leafs play here, enough said really. But it's a great place to watch a game (if you're able to somehow magically get tickets). It's also a great place to see a concert, especially compared to the Skydome. The sound in the Skydome isn't great for concerts, but the ACC is good.
If you're downtown, you should check out the Air Canada Center, home of the Toronto Raptors Basketball Team.