I'm very biased, since I'm actually chairing this conference, but PICC'11 ( http://www.picconf.org ) is in New Brunswick, NJ on April 29-30 of this year. 

We're trying to encourage both Windows and Linux admins to come. 

In addition, on the Pacific NorthWest, there's the Cascadia IT Conference ( http://www.casitconf.org ) that will be very similar in feel to PICC, since both are LOPSA-chapter organized community conferences. 

Attend whichever is closer to you, and meet the people you work near. Become part of the community!