moodle but not needing a host server to use. It's a free site as well. You create a workspace in your account and from there you can add a lot of different tools: syllabi, files, pages, etc. The site has a lot of potential for the classroom as well as for the media center. I can see it being used as a group wiki space for PBL projects.
Since my focus next year is going to be more PBL based, I am thinking I will rely on PBWorks a lot next year to get my students communicating with each other and doing more useful tasks.
I am also going to set up a workspace for the Media Center. I would love to start doing some online book chats, some informative tip sheets and maybe even a place for recommendations. I can't wait to get started. I think this will be a very useful tool for my students.