Writing Excuses http://www.writingexcuses.com/ Writing Excuses is a weekly podcast with four hosts (three novelists and one cartoonist) who discuss writing in a panel-style discussion. While the podcast is focused on fiction writing, I think they have a lot of good generalized material that is applicable to screenwriting, particularly this year (season 10). In January they began what they're calling their master class in genre fiction with each month focused on a topic area. January focused on generating story ideas; February focused on character development; March on story structure; April on beginnings (that is, story openings); May on world-building; and June is concerned with scene development. Each episode is short, usually kept between 15 and 20 minutes.

If you want to write comedy -- Writers' Bloc is a must.

Curious About Screenwriting Network KCRW's The Business On The Page with Pilar Alessandra Scriptcast

I listen to Marc Maron's interviews on occasion. For example, he had a good one with Paul Thomas Anderson. Thanks for the news about the WGA podcast! I couldn't find a way to download them as mp3 files, but looks like a really good one.

Not so much a 'writing' podcast, but HOW DID THIS GET MADE is hilarious as it breaks down movies' most absurd and illogical premises and storylines. I'll admit it has made me question my own scripts recently by asking 'what would they say about this scene'?