American Automobile Association - http://www.aaa.com/
Canadian Automobile Association - http://www.caa.ca/
Both clubs above offer maps, travel planning, etc.
Greyhound - http://www.greyhound.com/
Other bus lines - http://dir.yahoo.com/Business_and_Economy/Shopping_and_Services/Travel_and_Transportation/Bus_Lines/
Amtrak - http://www.amtrak.com/
Other train lines - http://dir.yahoo.com/Business_and_Economy/Shopping_and_Services/Travel_and_Transportation/Trains_and_Railroads/Passenger_Trains/
Alamo - http://www.alamo.com/
Avis - http://www.avis.com/
Budget - http://www.budget.com/
Dollar - http://www.dollar.com/
Enterprise - http://www.enterprise.com/
Hertz - http://www.hertz.com/
National - http://www.nationalcar.com/
Rent-A-Wreck - http://www.rentawreck.com/
Thrifty - http://www.thrifty.com/
A more complete listing of car rental agencies: http://dir.yahoo.com/Business_and_Economy/Shopping_and_Services/Automotive/Rentals/
Subways, light rail, heavy rail, buses, trolleys - Check the website of that city's public transportation system. A good site is http://www.nycsubway.org/. It's got listings of just about every place with a subway around the world.