There are many time servers around the world that provide reliable time by using NTP (Network Time protocol). Everyone can connect to these serves and receive exact time via this simple protocol. Read more about how does it work in http://www.pool.ntp.org/.

Guido Socher from tuxgraphics.org has built nice simple NTP client that can request for time packets from server and display this data on LCD.

He used one of his AVR ethernet boards where simple server application allows easily configure clock settings like NTP server address, time offset, Clock address and more. The web server has also a second page where current time is displayed – the same as on LCD. Author provides ideas on how to build clock, ad even provides source code, but if you just want to have this clock on your table really fast on then buy a kit from http://shop.tuxgraphics.org/ and support Guido for his nice ideas.