If you travel a lot, or are taking a trip across time zones and currencies, keeping track of things can get stressful. Mytravelr is a free app for your phone that gives you important data, like weather, time and daylight hours, international call codes and a currency converter.
MyTravelr has a neat tabbed interface, so you can flick side to side between the five different parts of the app. You can set your "home" location, and on the front clock page five clocks will show you the time wherever you want. The next tab gives you a five day weather forecast for your home city, while clicking up and down moves you alphabetically through all ther cities on offer. That's bad, as there are thousands of locations worldwide, and you can't choose to scroll through a personal selection.
The third tab simply shows you how much daylight you have in your current location, which is neat if you're in a new place, disoriented from jet lag. The currency converter is fairly standard, but does let you convert among three currencies at once. Lastly, there's a comprehensive list of international phone codes, along with that location's time zone, which might be useful for phoning home at the right time!
Mytravelr is a nice free app, that's only flawed really by needing internet access, which can be very expensive when you are abroad!