NTP.org – The home for the NTP Project who provides support and additional development resources for the Official Reference Implementation of NTP.
NTP Project support pages
THE NTP pool – list of public servers
NPL – The National Physical Laboratory in the UK who control the MSF radio signal.
The University of Delaware and David Mills’ information page, Professor Mills is the original inventor and developer of NTP
David Mills’ list of Public NTP Time Servers a list of public NTP servers
National Institute of Standards and Technology (NIST) who operate the USA’s WWVB radio signal
Europe’s largest supplier of NTP server related products.
Galleon UK – NTP server products for the UK
ntp-time-server.com – one of the largest time and frequency suppliers in the United States
NTP – Wikipedia article on NTP
NTP server checker – free tool to ensure time server accuracy