The Worldwide Coordinate Converter
The Worldwide Coordinate Converter is a nice tool to convert data between different geodetic systems.
To use the converter select the reference system of your data and the reference system you want the data converted to. You can then enter the coordinates manually, click on a Google Map, or enter an address. Finally, when you press convert, your coordinates will be returned in your chosen geodetic system.
The converter can also accept data with comma separated values (CSV).