Well, there's STA, but I've found that they're often not the cheapest (though they did get me a sweet deal to europe a few years ago).I would recommend using a consolidator to get an idea of prices (I use kayak.com - they have a lot of really useful features). Next, if you have a specific idea of where you want to go, search online for small discount airlines - their flights don't come up on consolidator searches. For example, if you want to go to europe, depending on where you are flying from, you may get a good deal if you fly Aerlingus to London, and then use discount airlines to get to where you really want to go in europe., Vivaaerobus is having a $9.99 special betwen Austin and Cancun or Monterrey, etc.If your time and destination is flexible, airhitch can be great for trips to hawaii or the caribbean/mexico. Their website is a pain to navigate though.Have a nice trip!
These offer tickets for students and youth (under 26) with more flexible terms, however, you should shop around because they have different offers at different times:http://www.aesu.comhttp://www.studentuniverse.comhttp://www.travelcuts.comhttp://www.statravel.comhttp://www.generationfly.comhttp://www.airtranu.comhttp://www.kilroytravels.comStudent tickets aren't always cheapest, just more flexible. If your travel dates are firm, then check hundreds of other sources with just a few clicks at http://www.bookingbuddy.com
your best chance is to research. you can try one of the sites i use because their easy and loads up pretty fast with all the companys on one page. Just check out my profile for a link.