Update: some of you may not see this new feature yet; we are rolling it out over the next week.

Administrators can now map public sites hosted on Google Sites to their own domains. Sites can be mapped individually to a specific URL, like http://www.example.com, and as a group under a specific URL, like http://sites.example.com/[name of site].

Editions impacted:
Standard, Premier and Education Editions

Languages impacted:
US English

How to access what's new:
Sign in to the control panel and choose 'Sites' from the 'Service settings' menu. Click the 'Web address mapping' tab and configure the URL where you want your site to be available.

For more information:
http://sites.google.com/support/bin/answer.py?answer=99448