US air-ticket??

I would recommend www.travelocity.com , I bought tickets from this website few times, prices are cheaper and service trustworthy.

If you don't mind flying anytime/any dates, you can use www.priceline.com. I bought from this website once, the price is cheapest. they will give you cheapest available flights to your destination, but cannot choose flight time (can choose flight date).

also, other advised by friends and my own experience.
www.expedia.com (normally more expensive than others)
www.orbitz.com (more expensive)
www.cheaptickets.com (my friend used it and okay price)
www.lastminute.com (sometimes has discount tickets)

如果你想最平GE...
又5介意可能要轉機GE...
去CHEAPTICKET.COM
禾之前刀有試過用佢泥訂機票"

一般去lastminute.com 或者ratestogo.com之類既網站會最平~不過要日日(甚至every few hrs)check住~