PrintBureau is an app that enables to print directly from the iPad where Wi-Fi network is available. It can also works on Bluetooth and USB cable using the free print server software.
It prints via 3G/EDGE too. It features to print from pages/numbers via mail, transfer docs and files via iTunes using USB cable, open documents stored in PrintBureau directly into iWork for easy editing, open files stored in the cloud (iDisk or WebDAV service) directly into iWork. The app costs 13 dollars. [link]