I am testing using google sites next year with my class to see how that works. If it flops I will definitely have to check out some of these other options!
I began the year using PBWorks, which I still love, and you can view initial student portfolios here. I later found out, however, that Wikispaces had made many improvements since the time that I had first investigated them (@ two years ago), the best of which was a new feature which allowed students and teacher to leave in-line commenting. I therefore had students move their portfolios in early spring to this new location, although earlier pieces still reside at PBWorks. You can see what types of writing/reflection pieces were included in this year's portfolios by visiting the Teacher's Notes page.
I love wikis in that they truly organize student work, allowing for both increased audience and peer feedback. All sorts of multimedia tools can be easily embedded, which keeps students in a fairly closed, safe work environment. Protocols and procedures, once in place. make it a wonderful work environment.