I have my own wiki that I use like Blackboard for my work with KICKS. I also have one for Warriors of the Dance and for my grad school portfolio. Students can only see these wikis if you give them the link, so sometimes handy for communication that students DON'T need access to!
Here is the link for my work with KICKS: http://kicks2earthspace.wikispaces.com/
Here is the link for Warriors of the Dance: http://warriorsofthedance.wikispaces.com/
I prefer wikispaces as a wiki hosting site. You can get an educators free liscense and you/your viewers won't have banner ads. I have lots of documents/videos, etc. and haven't hit the data limit yet.
I still am reluctant about using them in class, so for that using the school wiki would be good. A little more contained for sure! Although sometimes I think wikis are another form of blackboard, depending on how they are used. (which is what I need more practice on!)