Hasin Hayder has posted an example of a "world time search" he's worked up that uses the geonames.org and Yahoo! developer APIs to pin down the time at any given location.

I recently came by this site WorldTimeEngine where users can search the local time of any place using the name, street address or just latitude and longitude. Since that time I was thinking how easily you can make your own. As long there are some good people over there (For Geocoding API) - its a not a big deal, you know?

His script pulls the location of the place (latitude/longitude) from the Yahoo! geocoding API and passes that back into the geonames web service to get the local time. The result is an array with the lat/long, address you submitted and the time output in a standard string.