The public libraries have free locations if the event is free and open to the public. One member had a Biznik event in a large room in the basement of the Fremont Library - seems like it could hold 30 comfortably.
Espresso Vivace on the corner of Denny & Broadway has a great roasting room that seats a dozen. I believe it has the same policy as the room in Uptown Espresso, first come first serve, sign up by the door.
The new Elysian Fields bar/brewery/restaurant down by Safeco Field has a large space in the back facing 1st Ave S. I attended a birthday party there - don't know about fees or WiFi.
COMING SOON on the new web site:
A listing of venues perfect for Biznik events that can be edited by our members, with rates, hours, WiFi and contact information.