Hero and Boojum, I think this might be what you're looking for:
I'd read the whole thing, but know that the good stuff on formatting dialogue starts about halfway down the page. I have no idea which studios use these formats, or whether it's hopelessly outdated and something ever so much whizzier and cooler has been introduced, but it's a start.
Critiques from more experienced members welcome, of course. Hope this helps.