I would use Google Sites.
It's one of the core Apps in Google apps and it's heavily integrated with Docs so you can post them to pages etc.
Set up an easy to remember subdomain like wiki.yourdomainname.com for your google site and then share the site with your domain account members if you need security. Make it public for clients or just parts of it. More on Google sites: http://www.google.com/sit
You can start creating a Google Site by visiting sites.google.com
Or just click the "sites" link above your Google Apps mail inbox.
