Make timezone dropdown list populate with available timezones on a per Country basis?
I just noticed something really nice on the Google Analytics signup page for adding a new domain. First you pick a country them you pick your timezone. Instead of showing a huge Timezone list though they populate the timezone list with only timezones that are available for the country you have selected. I think this is a great idea to make picking a timezone easiar for some users.
Can't help with jQuery but for how to figure out what timezones are in each country, you can use DateTimeZone::listIdentifiers() with DateTimeZone::PER_COUNTRY as first argument and the ISO 3166-1 compatible country code as second argument, e.g.
Note: PHP 5.3 is required.
You can construct the data you want from this table: http://www.datelib.de/Timezones.shtml.en. You would simply group by the Country code column. Probably the best way to go would be to throw all this data into a database table and use some AJAX magic to handle select menu onchange events.