Although the deadline for the 2009 contest has not been posted yet, the submissions are usually due by October of the year before GDC -- so plan ahead!
Submission rules from last year:
Open to all independent game developers worldwide
Seumas McNally Grand Prize ($20,000)
Excellence In Visual Art ($2,500)
Excellence In Audio ($2,500)
Innovation Award ($2,500)
Technical Excellence ($2,500)
Best Web Browser Game ($2,500)
Audience Award ($2,500)
Note that there is a specific student competition:
Best Student Game = $2,500
Student Showcase Winner = $500
All games included in the showcase also win a conference pass, some expo passes, and some additional money for travel.
Student specific rules:
Winners in 2008: