Of course, you can print from iPhones and iPads if your printers support their AirPrint standard - but, inevitably, neither of mine do. (Printer aficionados might spot that my laser printer is around 15 years old.) However, I can now merrily print from the iPhone and iPad anywhere in the house, thanks to a nifty little package called Printopia.
This isn't an app - I use the standard 'send to printer' option from the mobile device. But Printopia is a cunning little add-on that sits on my Mac, which brings up my printers (and optionally various other destinations, like sending the print to Evernote or the computer) as if they were the real thing.
There's a free trial version, but it's one of the few add-ons I have willingly paid for, because it is solid and it just works. Once it's installed, it's controlled from the standard Mac settings panel (shown above) - but you rarely have to do this, because Printopia is transparent - it just lurks in the background and pretends to be AirPrint printers.
Of course, because the add-on runs on a Mac you have to have a Mac on the same network as your printers and it has to be powered up (though not active - Printopia works fine if the Mac's asleep).
I know 'people who use iPhones/iPads and have a Mac on the same network as their printers' is probably a relatively small cross-section of the world. But for those of us who fit in this niche, Printopia's well worth a try.