Now have custom URL (in your domain) for your site created using Google Sites

Now Google Apps domain administrators can 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].

So in your company if you have a site each for HR, Marketing, etc you can now have URLs like:

http://hr.example.com
http://marketing.example.com

and these URL will be diverted to site created using Google Sites. However to do this you will need admin access. So only your domains admin can set these URLs from admin control panel.

Read more on Google blog
Google Sites Blog: Google Sites on your domain