Windows: Whether you're just printing an individual photo so you can frame it, or you want to fit several smaller pictures on a single sheet, few programs make it as simple as Primg.
The interface is straightforward and practical. You find the folder with the photos you want to print in the left-hand column, preview your layout in the middle, and make adjustments on the right. You can choose to print thumbnails of multiple photos, a single large print, or smaller tiles of the same photo. The right-hand column lets you choose exactly how large the photos should be, and how many you want on the page. When printing a single photo, you can also drag it freely around the canvas to get it properly positioned. Once everything's ready to go, just hit print, and you're done.
Of course, you could get a little more control creating a layout in Indesign or Publisher, and most photo managers have some built in options as well. But if you just want to print the photos and be done with them, Primg should be all you need.