Xeriom Time Service
We run a local NTP server on time.xeriom.net.
If you're using the XeriomUbuntuPackagesService then you can install the xeriom-ntp-client package. Otherwise there's an article about how to setup NTP on my blog at http://barkingiguana.com/2008/08/02/using-ntpd-in-a-ubuntu-804-xen-virtual-machine