Practically, all you need is drivers license + birth certificate. Officially, I believe the rule is that a US citizen only needs birth certificate, but they have the right to require a passport to prove you are a US citizen
The rules are the same for Canadians going down to the US. I normally bring my passport just in case but have never had a problem with just license & birth certificate.
I live in Toronto so I never know about anything interesting except when someone comes from out of town with a list of interesting places to see...
