Theater Communications Group organizes an annual free theater night for some areas around the country. Show locations and info are listed on the site linked below - tickets become available early in October for performances in mid to late October.
"Free Night of Theater is TCG's exciting national audience development program designed to attract new audiences to America's not-for-profit theatres. Since the pilot program debut in 2005, Free Night has increased in scope and participation each year...
In 2007 the Free Night program will be presented in Atlanta, Austin, Boise, Cincinnati, Cleveland, the state of Connecticut, Indianapolis, Kansas City, Lexington, Los Angeles, the state of New Jersey, the state of North Carolina, Oregon (in Ashland and Eugene), Philadelphia, Sacramento, San Diego, San Francisco, Seattle/Greater Puget Sound, South Carolina, Charleston, several states represented by Southeastern Theatre Conference, Washington D.C. and the state of Wisconsin."
http://www.freenightoftheater.net/shows/index.cfm