Cheap Flights

Most people know about Travelocity and the other search engines for plane tickets, but I stumbled upon this site the other day: www.sidestep.com

It searches not only the main commercial airlines, but also most of the discount ones as well.  It's given me the lowest price on the last two flights I've booked. 

Technically, I don't the tickets through this site.  I just found what airlines were the cheapest, and then went to those direct sites.  It's usually a bit cheaper that way.