For residents of Ontario, Canada (of which I've seen more than a few on the board here
) there's a very handy, printable PDF that summarizes photographers' rights.
http://www.oshawacameraclub.ca/references/ontphotogrights.pdf
The TL;DR of it is, if you can see it, you can shoot it, even including things like crimes, accidents, police, etc. There are a few exceptions, such as minors charged or convicted of crimes, people with reasonable expectation of privacy (no shooting through peoples' windows), and people endorsing a product (requires a release). Otherwise, it's pretty much fair game. I
always keep a couple copies of this in my bag, both for people who might have misconceptions about the law, or for potential police harassment.
Digressing for a moment from shooting people, and more about shooting places, the law here in Ontario has an interesting limitation. Should one decide to trespass on private property for the purposes of photography, and not get caught, you can freely use those pictures if you sit on them for 6 months after the intrusion. A footnote for any urban explorer types.