http://support.ntp.org/bin/view/Servers/NTPPoolServers

pool.ntp.org uses DNS round robin to make a random selection from a pool of time servers who have volunteered to be in the pool. This is usually good enough for end-users. The minimal ntpd configuration file (e.g. /etc/ntpd.conf) for using pool.ntp.org is:

driftfile /var/lib/ntp/ntp.driftserver 0.pool.ntp.orgserver 1.pool.ntp.orgserver 2.pool.ntp.orgserver 3.pool.ntp.org

 Any questions about the pool.ntp.org server pool should be directed either to the pool mailing list or to the comp.protocols.time.ntp usenet newsgroup.

 Time server operators are encouraged to visit the NTP Pool web-site to find out how they can join the NTP pool.

The NTP Pool DNS system automatically picks time servers which are geographically close for you, but if you want to choose explicitly, there are sub-zones of pool.ntp.org. The “continent” ones are:

Area:	HostName:
Worldwide	pool.ntp.org
Asia	asia.pool.ntp.org
Europe	europe.pool.ntp.org
North America	north-america.pool.ntp.org
Oceania	oceania.pool.ntp.org
South America	south-america.pool.ntp.org

There are also sub-zones for many countries. Click on your continent to see which country-zones are available there.

When using the by-country zones, be careful: some of them currently contain only one or two servers, so you are probably better off using either the zone of a nearby country, or using the continent or global zone (This is sometimes also valid if you live in a big country). In general though, just use the “global” zone as in the suggested configuration near the top of the page and let the system sort it out for you.