Blogs
Blogs are an effective form of social media. We're big believers in the corporate blog. It's a direct line of communication with clients.
Corporate blogs aren't just for commercial enterprises. Non-profit organizations can and do leverage blogs very effectively. Those that have an affinity for a non-profit's mission want to be up to date on pertinent issues, trends, and are generally interested in the opinions of a leader in that field. Blogs make it easy for supporters, volunteers, etc. to stay informed. Further, your messages serve as a superb mindshare development tool.
The best blogs are generally content driven, meaning they are updated "as events warrant", not conforming to some pre-defined schedule.
At the discretion of the blog's owner, a blog may have one author or many. Blogs can include search functions or author filters.
Blogs are easy to use and inexpensive to setup. A web site can contain a link to an externally sourced blog (cost is virtually nothing) or can host its own blog, with or without RSS.
There are hundreds of free blog services, a sampling of the most popular can be found at...
www.wordpress.com comprehensive set of tools
www.blogger.com great for beginners
www.blogspot.com also good for beginners