Beagle Software
   NTP, Daytime timeserver and client software and hardware.
   http://www.beaglesoft.com

Brandywine Communications
   Offers advanced off-the-shelf and custom hardware time and frequency solutions including Network Time Protocol servers.
   http://brandywinecomm.com/

Configuring Microsoft's Win32Time service.
   Useful information on how to configure the win32time service which ships with Microsoft's server products.
   http://support.microsoft.com/kb/314054

ELPROMA NTP Servers
   European manufacturer of NTP Time Servers.
   http://www.ntp-servers.com/

EndRun Technologies
   Provider of time and frequency equipment including NTP Servers.
   http://www.endruntechnologies.com/

Galleon Systems
   Provider of NTP time synchronisation solutions using the MSF radio signal and GPS satellites.
   http://www.galleon.eu.com/

Meinberg USA
   Manufacturer of hardware Network Time Servers (NTP) for IPv4 and IPv6 networks.
   http://www.meinberg-usa.com/

NIST Web Clock
   Shows the official US time in each time zone.
   http://www.time.gov/

NPL Computer Time Services - Truetime/NPL Phoneclock
   Synchronization to UK time by telephone. This is the UK's national measurement laboratory.
   http://www.npl.co.uk/server.php?show=ConWebDoc.995

NTP with TymServer
   Hardware NTP time server manufacturer.
   http://www.tymserve.com

Network Time Protocol (NTP) Project.
   The official page for the NTP Project. Contains information about the project, reference implementations of the protocol and software links. Also links to the pool of public NTP servers.
   http://www.ntp.org

Open NTPD
   A mainly BSD implementation of the Network Time Protocol.
   http://www.openntpd.org/

PresenTense Time Server
   Multi protocol time server which synchronizes itself with any true time source, including GPS via rs-232 com ports and then acts as a time server for all network clients. PresenTense Time Server ships with drivers for many reference clocks including Spect
   http://www.bytefusion.com/products/ntm/ntm.htm

Spectracom: GPS hardware NTP and SNTP clocks.
   Manufacturer of hardware GPS clocks and NTP/SNTP servers. Legally traceable time.
   http://www.spectracomcorp.com

Symmetricom, Inc.
   Manufacturer of time and frequency synchronization equipment, including NTP Servers.
   http://www.symmttm.com/products_network_timing.asp

TimeTools
   Specializes in computer and network timing solutions. Using NTP for network time synchronisation in conjunction with MSF, DCF-77 and GPS time sources.
   http://www.timetools.co.uk

Timeserver description on Wikipedia
   Some useful information about the basics of what a time server is.
   http://en.wikipedia.org/wiki/Timeserver