CheapTickets.com - http://www.cheaptickets.com/

Discount Fares - http://www.discountfares.com/

Expedia - http://www.expedia.com/

Mobissimo - http://www.mobissimo.com/

Orbitz - http://www.orbitz.com/

PriceLine - http://www.priceline.com/

SideStep - http://www.sidestep.com/

Smarter Travel - http://www.smartertravel.com/

Travelocity - http://www.travelocity.com/

TravelZoo - http://www.travelzoo.com/

Uniglobe Travel - http://www.uniglobe.com/

Yahoo Travel - http://travel.yahoo.com/

More methods of transportation and reservations -

http://directory.google.com/Top/Recreation/Travel/Transportation/