I know that twitter gets a lot of coverage as part of the PLN discussion, but I thought this topic fits better with online learning, so I'm posting it here.
I recently started following the hashtag #edchat, setting up a column on Tweetdeck so that I always see the latest posts.
Here's a link to someone's explanation: http://teacherbootcamp.edublogs.org/2009/07/30/what-is-edchat/
It is, simply put, a fantastic way of keeping up to date with some leading thought and ideas regarding education. Very impressed. Anyway, shortly after following it, I discovered a whole bunch of new tools and articles that were worthwile reading.
Here's an example: Mouse Mischief (http://www.microsoft.com/multipoint/mouse-mischief/)
Teaching in the 21st Century (http://simbeckhampson.amplify.com/2010/04/27/teaching-in-the-21st-centur...)
Highly recommended that you take a look, if you haven't already.