Woke up to find Google Sites has been released for Google apps. Logging in to Google apps I couldn't find where I can start using Google Sites. Turns out you have to add the service from a link right above your existing services. My existing services were start page, chat, web pages, email, calender. I had two more services that I could add. Google Docs and Google sites.
I just had a few minutes to play, looks like a nice wiki tool for your site. You'll find more information here.