www.hotwire.com
www.lowestfare.com
www.cheaptickets.com
http://edit.yahoo.com/config/ytravel?resform=YahooFlightsR

...you can sometimes get the best price by directly booking at the airline's website. Check the discount websites 1st, then hit Yahoo/Travelocity, then check the airline websites, THEN go to the airpport ticket counter. The last option has been the cheapest ticketing price that I've found for 3 out of the last 4 plane tickets that I've bought.

The deep discounters only let you choose the days you travel, no real discount if you need to choose the arrival and departure times that are anywhere close to those that fit your needs before committinng to buying the ticket. An example: If I wanted to fly into Vegas tomorrow for two days, the discounters might find me a flight that leaves here at 9:00 pm 05/08/01 arriving in Vegas at 11:59 pm , and the return flight could be a 6:00 am 05/10/01 outbound flight. That realistically gives you one day at your destination, the airline fills a seat, and the discounter makes a few bucks in the process.

Bob