Where can I find information on passport requirements for traveling between the US and Canada?

you can find all information you need online

General information can be found at: http://travel.state.gov/

There is specific information about changes in travel to Canada at: http://travel.state.gov/travel/cbpmc/cbpmc_2223.html

The regulations vary depending on when you go and if you fly or travel by land/sea, but you pretty much need a valid passport.