There is a great wealth of skeptical content on the web, and it is constantly growing. New skeptics wanting to get involved often choose blogging or podcasting as a "default" way to get involved. In this SkeptiCamp Atlanta 2011 presentation, I recommend against that and suggest at least eight other online activities instead.
Audio is available in Skepticality #158 Return to Lake Skepticamp. (Note: I fixed the seven/eight typo you will hear mentioned in the audio in these slides).