Readdle's Printer Pro for iPhone is usually $4.99 but right now you can grab it absolutely free for the iPhone. I'm not sure exactly how long the sale lasts — iTunes says 24hrs, Twitter says 48hrs! — but act fast because either way, it won't last long.
Printer Pro for iPhone does more than just AirPrint. Essentially turns the iOS "Open in..." dialog into a print dialog so as long as you have a printer attached to your network somewhere, there's a good chance you can turn the file on your screen into paper in your hand with just a few taps, with control over preview, range, layout, scale, and more.
If you like it, you can also get the iPad version for just $2.99 as a way of saying thanks to the fine folks at Readdle!