Script Formatting

There is no absolute "standard" format used by all professional screenwriters working in the American film industry. Slight variations abound in scripts written by professionals.

Some good links on Script Formatting:

INTERNET

Screenwriting in Style has various sections and many useful tips

The Nicholl Fellowships in Screenwriting provides a good insight with a Screenplay Format Example

Scriptologist How to Format a Screenplay Part 1
Scriptologist How to Format a Screenplay Part 2
Scriptologist How to Format a Screenplay Part 3

US Screenplay Presentation

BOOKS:

The Screenwriter's Bible: A Complete Guide to Writing, Formatting, and Selling Your Script

The Complete Guide to Standard Script Formats: The Screenplay
(but beware: it was written in 1983)