Print pics directly from your iPhone or iPod Touch with Air Photo
There are two components to Air Photo: the server (a free download and runs on both Windows and Mac) and the client app, which you'll find on the App Store (just search for air photo).
In a single-server setup, the app will automatically connect via Bonjour - otherwise you can use the connect button to specify the server you'd like to use for printing. Press the print button, and your server's Air Photo window will activate. It automatically selects landscape or portrait orientation and allows you to scale images or leave white space.
At $1.99, the app is a great buy - especially if you print a lot of images that you've saved on your iPhone or Touch.