PBWorks really works. After some research, I prefer using PBWorks to Wikispaces. Visit Classroom 2.0 for some other opinions on this topic.
I recommend setting up a free educator account and exploring how you can use this tool to get students engaged with content and writing, as well as collaborating and sharing with each other.
My page is here. You will notice that each student page is in its baby stage. Check back at the end of June 2011 to see what my students have done.