I'll also post this on my screenwriting blog, http://www.screenwritingsuccess.com, but I thought it belongs here, too--people frequently ask me what screenwriting format software to use. The industry standard is Final Draft, but it's not cheap.
I've recently run across at a very simple to use free online tool at www.rawscripts.com. There's only one format (screenplays). It saves your script on their site, not on your computer (although of course you can download a copy and you should). You can import or export from other formats, including Final Draft.
I"m experimenting with it at the moment and my first impression is positive--if you're in the market, give it a try.
