Wikis are great. I've started to use them on several collaborative projects that I'm involved with at present. I'm currently working on moving the Tech Notes from PLA over to a wiki format, via MediWiki on the Best Practices for Libraries Wiki. I have created, via pbwiki, one for an Internet Librarian 2006 presentation that I'm working on with a colleague who lives in Chicago. My colleague, Kelly C. here at PLCMC, has created one, using pbwiki, that we are working with for the Teen Second Life Library project that we are working on here at PLCMC with the Alliance Library System. Then, lastly I've started to mess around with Confluence for an internal project within our Technology Education Department here at PLCMC.
They are excellent collaborative spaces to work within.