1. Product documentation — collaboratively write it in-house, then let customers add to it as they use the product.
2. Collaboratively write news releases — A great way to make sure that a news release has input from product managers, marketing staff, etc. and can be quickly updated as necessary before release.
3. Knowledge base — Keep common FAQs and support questions on a wiki so they can easily be updated with new information.
4. Meetings — Instead of emailing agendas that can't be easily and quickly changed, put them on a wiki page. Take meeting minutes on the same page and you'll have everything on one place!
5. Manage projects — Give each project a page in your wiki, and keep all relevant materials there so it becomes a magnet.
6. Build a peer-directory — This gives people a reason to come to the wiki in the first place — to put information about themselves in the directory — and then they stay to collaborate.
7. Keep time-sensitive information up to date — For example, I keep a list of events where I'm speaking on the wiki, and others can add an event they want me to know about.
8. A space for every group/team/department — Give each group a place to organize their projects and work collaboratively.

Which ones do you want to know more about? Vote in the poll below and I'll write in-depth posts about the four uses that get the most votes: