Taxis are available in Baltimore 24 hours a day at all hotels and at the airport.  Several taxi companies work in the city, but one of the biggest is Yellow Transportation.  Their taxis are available by phone 24 hours a day at 410-685-1212.   

Rental cars are available from all major US rental companies at the Baltimore/Washington International Airport (BWI) as well as in the city itself.  Car rental companies have offices in many hotels, while  Enterprise and   Budget have several city locations.