The free scriptwriting and film production package "Celtx" has reached version 1. I've been using it for over a year, and I like it a lot though it's unlikely I'll ever use all the film production facilities.
It allows you to create screenplays, stage plays, radio plays, comic scripts and AV scripts. It's intuitive to use and allows output as PDF. It also allows collaboration and sharing of scripts online with as many or as few people as you like. It will print scripts as either A4 or foolscap.
On the production side it generates all the sort of stuff needed by the various departments in as much detail as you need, depending on how big your production is.
It's not perfect, my biggest problem is that the PDF formatting is not absolutely identical to the on-screen formatting so in a feature script there's a few pages discrepancy between how many pages you think you have, and how many you do have.
But this is not too serious. And it's free!
If you haven't plumped for a specific scriptwriting application, plump for this one.
What's on the turntable? I'm listening to an unabridged reading of "Day of the Triffids" by John Wyndham. What a genius.