The Royal Observatory Greenwich has a wide-ranging treasure trove of information on time & Astronomy.
British Horological Institute - packed full of materials and links
The Sundial Trail at the Horniman Museum in London, England a comprehensive information site from the British Sundial Society
Compute Local Apparent Sidereal Time that is the actual time for your spot on the globe in relation to Greenwich. Outside the USA you will have to know your longitude (that's the East, West one!). Greenwich is at zero degrees Prime Meridian of the World.
Clocks and Time Tools
Our creative collection
What time is it?