Playbill.com posts all the theater jobs, so I go there.
My other standards...
I go through Craigslist and have only been applying to things that sound halfway legit because there is a A LOT of garbage on there.
Same with Monster.com and Careerbuilder.com. I am upset HotJobs has combined with Monster.com...I liked the old HotJobs.
I also go on individual websites for publishing houses and Time Warner. (Which is the most beautiful building.)