The Game Developers Conference (GDC) is the official trade event "by developers for developers" of computer, console, mobile, arcade, online games, and location based entertainment.
Official Website: http://www.gdconf.com/
Added by tonys on July 3, 2007
I was lucky enough to go last year. Definitely check out the Indie Games Summit and the Experimental Gameplay Workshop if you're going this year.
For those interested in software security, consider attending local OWASP meetings. They are free...
Ill be their for a few days provided im not snowed in at tahoe.
If your interested in games outside of hardcore - also consider Monday & Tuesday's Worlds in Motion Summit. It's part of GDC but focused a little wider on social games (facebook), casual MMOs, virtual worlds, and the "edge" of gaming.