Today's XKCD really is wonderful: called Now, it's a simple clock which shows you what time it is in the world right... now, and changes each time you check back on it.
It's created in such a way that it's super simple to read. Noon and midnight always sit in the same place, and each time you visit the place names and maps of the world will have shifted to show you what time it is, everywhere, right now. Super simple, super effective. Go check it out. [XKCD]