Theatre Communications Group (www.tcg.org I think) publishes American Theatre magazine as well as Artsearch which lists job openings at member theatres across the US. Artsearch is not cheap (TCG by comparision is), but libraries sometime have subscriptions. The NY Public Library has a subscription.
TCG also publishes plays and books.
This is the first magazine to get.
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher