The Toronto Humane society is a great charitable organization in Toronto. Unlike many shelter environments, THS is a happy place where animals get treated better than in some homes (how many people take their dogs for walks 7 times a day?). The turnover rate is quite high, with dogs being in the shelter for 2 or 3 weeks usually and they've got such a low euthanasia rate it is classified as a non-kill shelter (under 3%).
The volunteer process is quite lengthy, so if you want to get involved be sure to keep an eye on the website for orientation sessions as they don't happen more than once a month generally.
Well worth the time to stop by and check out if you're considering a pet to help care for on site, to foster, or to give a permanent home.
Bonus: right across from The Beer Store.