Origins is a gaming convention held each summer, sometime around the 4th of July, in Columbus Ohio. This year it's June 25th through June 29th. Generally they have tens of thousands of gaming enthusiasts show up for four days of little sleep but lots of fun.
I go mostly for the role playing, but there are board games, card games, strategy games, word games, pretty much anything game oriented you can think of.
Here's the link to the convention page: http://www.originsgamefair.com/