Hewlett Packard has this nifty little app called HP ePrint that does wireless printing. iOS devices are already capable of doing that out-of-the-box (with iOS 4.2 and newer versions), but if you want more features, HP has you covered.
HP ePrint lets you print from your iDevice over Wi-Fi, via the Internet to an HP ePrint printer, or directly to HP wireless direct supported printers.
You can also access HP Public Print Locations (print/copy stores, hotels, and airport lounges), and you also get support for HP ePrint Enterprise (service and Internet purchased separately).
Version 5.2.0 of the HP ePrint iOS app brings faster processing of print jobs for many file types, performance improvements to web printing, support for the iPhone 5 screen format, improvements for iOS 6 users, miscellaneous enhancements (on the visual front), as well as minor bug fixes, for more stability.
Download HP ePrint iOS (Free)