In addition to statravel.com, travelcuts.com, studentuniverse.com, and LH's generationfly.com are worth a visit to see what they have on offer for cheap/free return date changes.

STA and Travelcuts will require the student travler have an ISIC card ($22 to purchase, and it actually includes some decent basic travel insurance). Studentuniverse and generationfly require student ID/status, but no ISIC.