John Tropea has written an excellent article on using a blog and wiki for support knowledge, and I recently left this comment on his blog:

One of the best wiki uses for support staff is to build a central knowledge base so that people aren’t keeping the knowledge to themselves – which isn’t their fault, really. Until the wiki comes along, they have no good place to post the questions they commonly get asked, and the answers they’ve developed.

Once the wiki is in place, they can add these questions, and list their answers. Then, others can add to those answers, refine them, and make them more comprehensive as they encounter different scenarios, etc.

A blog can work hand in hand with the wiki as a means to call out content on the wiki and direct people to it. For example, if one person gets asked a particularly complex new question, they can post their answer on the wiki, then publish a quick blog post letting others know about the new question and asking if anyone else has answers to share. This is a great way to jumpstart contributions to a particular wiki page.