I say: why not Twitter? Now, there are of course levels of twittering and integration of twittering into your non-profit's business, and there may or may not be reasons to bother with creating and maintaining an active twitter "community," depending on your projects and audiences.
However, if you have an RSS feed of your organization's news; why not take a few minutes and set it up to also pipe into Twitter? You've immediately created a basic "mobile" strategy where people can sign up to receive news blurbs through SMS, enabled another path for people to get your updates, and it took almost no time, requires almost zero maintenance, and is free -- how can you beat that?
Of course, I'm just trying to make my Twitter-on-the-rise prediction for 08 come true, but I wrote late last year about the simple utility of Twitter as part of my overall "Write Once, Post Everywhere" (WOPE?) strategy.
Update: Nate Ritter has made a specific case for Twitter in disaster/emergency response, but also compiled some good ideas about integrating twitter as an outreach tool with other existing web 2.0 type services like flickr. Read more