Clear Timezones and jQuery
Makes it really easy to have a quick look at how times line-up around the world. For example, I've saved this link to see Vancouver (my sister), Melbourne/Sydney (most of the rest of the family) and Singapore (me) all in one go.
It's done in pure Javascript, and is a good example of jQuery in action if you care to look;-)
See also: timeanddate.com for encyclopaedic coverage of everything related to times and dates.