http://expedia.com/
http://priceline.com/

Sidestep is pretty good at shopping most of the sites.

do you hvae a flightcentre? if not,

www.flightcentre.co.nz

or mabye one in your area.

I spent HOURS one day searching every conceivable travel site looking for cheap plane tickets from California to Ohio. Every site came up with exactly the same price for the same flights. I was rather surprised. Although I do know that Orbitz has an agreement with their partner airlines that they have to offer Orbitz the lowest price on a given flight before they offer it to anyone else like Travelocity or Expedia. This also might extend to Hotwire since Orbitz partners with them.

I ended up going with Southwest because they were cheaper and offered more favorable flight times.

I absolutely love spiritair.com
Their regular airfare is reasonably priced but when they have sales!!! You can get flights for as low as 88 cents!!!

Check a new website www.vayama.com - it has some good deals, especially for international travel.

http://www.expedia.com/ has been my travel website for a few years now - fast, easy to use, the descriptions are accurate and I've never had an issue with them. They're especially good for if you will also be purchasing a hotel room, because you can get a discount on your plane tickets that way sometimes.

I have also heard good things about http://www.priceline.com,/ though I have never used it myself. That's the one where you can bid on tickets.

cheaptickets.com

http://www.mobissimo.com/search_airfare.php

http://www.kayak.com/

I found mobissimo.com to best suit my international needs.

If you check expedia and those you mentioned and then check the airlines directly online, you may fine a slightly better deal. Sometimes the travel site don't allow a cancelation and the airlines may.