Time

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/

Elproma
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/

How to Configure an Authoritative Time Server in Windows XP
Useful information on how to configure the win32time service which ships with Microsoft's server products.
http://support.microsoft.com/kb/314054

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

National Physical Laboratory - 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

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

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

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

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

PresenTense Time Server
Windows 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. Screen-shots, features list, documentation, and free 30-day demo version.
http://www.bytefusion.com/products/ntm/pts/whatispresentenseserver.htm

Spectracom
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

Time Synchronisation
Providing information about Time Synchronisation.
http://www.time-synchronisation.co.uk/

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

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