Etherpad is on both The Best Online Tools For Real-Time Collaboration and The Best Online Tools For Collaboration — NOT In Real Time lists. It’s a very, very easy way to collaborate in real time. You just paste a bunch of text in a window and, without even having to register for the service, send others the url and everybody can edit it in real time. It also has a chat option.
You can go back to the url address at any time to make further, adjustments, too.
TechCrunch has just posted about some changes Etherpad has made to become even better. Instead of repeating what they say, I’d recommend you either read their post or just go directly to Etherpad and try it out.