Prices are coming down as demand weakens, so if you were thinking of taking a flight — now might be a good time to start shopping for tickets.Southwest Airlines and AirTran have both announced fare cuts and the LA Times says that traffic is down 31% at LA/Ontario International Airport as ExpressJet, United Airlines, Delta Airlines, Southwest Airlines and JetBlue Airways have eliminated or slashed service. With that in mind, here are three shopping tools we like…