The Kindle 2 comes with a charger, but you might want an extra one for your office or to keep in your travel suitcase. Amazon provides an official Replacement Power Adapter for $14.99.
You should know, however, that the Kindle 2 charger is a different charger than Kindle 1. If you have a USB to mini USB cable already (such as for an mp3 player or camera), you can charge your Kindle by attaching it to your computer. While Kindle 1 could also be attached to your computer, it did not take a charge that way.