I run a couple of NTP pool servers and a monitoring page for NTP servers. If you want more info on NTP, you should go to http://en.wikipedia.org/wiki/Network_Time_Protocol. If you’re wondering whether ntpdate is good enough to keep your clock synchronized, don’t. It isn’t. Just go install ntp (or ntpd) and let it run.
Please do not use my NTP pool servers direct by IP address. They are members of the ntp pool. Use the pool instead. If you’re interested in joining the pool, the NTP Status page is a good resource for finding reliable upstream servers (the official page has a lot of dead servers).
My current NTP servers are a Raspberry Pi B+ and a V-Dedicated system from SpeedyKVM