Last week on National Public Radio, there was a short story about technology in the classroom which gave some press to wikispaces. The other wiki host mentioned was pbwiki.
As you can see in the column next to this post, I have a wiki on wikispaces, which has been working quite well for me. However, there was one disturbing discovery this week. Someone got into one of the member profiles and replaced a friend's photo with his own. I have no idea how this lurker/hacker managed to do it, but it's so thoughtless.
You should definitely check out Mr. Sheehy's wiki and blog. He's a high school English teacher in South Dakota, and he's using his wikispaces with great flourish, if you're looking for ways to use yours.