You can now play over 15 million Spotify songs on your computer for free in this country — partially because Spotify counts on the fact that if you get addicted to listening to music and building playlists on the service, you’ll want to play those playlists and listen to that music on other devices: your smartphone and your home stereo.

We count at least five great ways to play Spotify Premium within the home. This is no trivial matter for Spotify users, because music is greatly enhanced by the mechanics with which it is reproduced (which is why headphones are really important too).

The following Spotify players for the home are listed alphabetically under what we like to call the “different strokes” principle. For example, not everyone uses Apple iOS. What might be right for you might not be right for some.

Apple AirPlay

If you own an Airport Express or Apple TV (or AirPlay-enabled speakers or sound systems — more on those below), you can use Apple AirPlay to stream anything in the Spotify iPhone app to the best speakers in your house, whether they’re standalone, connected to your home stereo amplifier, or connected your television’s surround sound box. From where we’re sitting, Apple offers the best option for Spotify in the home if you already have the remote control (an iPhone or iPod Touch) in your pocket.

Maybe this is why Apple figures it doesn’t have to sell its own music subscription. It can sell more iPhones, iPod Touches, iPads, Apple TVs, Airport Expresses, and AirPlay-licensed hardware to subscribers to Spotify and other AirPlay-compatible music services — and even collect part of that subscription revenue in the process.

Denon and Marantz

This one’s also for Apple iOS users. Certain Denon receivers have built-in Apple AirPlay support, as do a few from its sister brand Marantz. By running the Spotify Premium app on your iPhone, iPod Touch, or iPad, you can stream Spotify to a wide range of Denon receivers starting at $600 the last time we checked.

Check out Denon’s line and Marantz’s line, if this approach of funneling Spotify through your iOS device to a home stereo system sounds right for you. One thing to keep in mind: Unlike the others, both Denon and Marantz charge $50 for an AirPlay firmware upgrade.

AirPlay-compatible speakers also include Bowers & Wilkins Zeppelin Air, JBL On Air Wireless, iHome AirPlay (coming soon), and we assume many other Apple partners to follow.

However, there are plenty of ways to play Spotify in the home over nice speakers even if you don’t use Apple iOS:

Logitech Squeezebox

Logitech purchased one of the earliest innovators in home digital audio a few years back: Slim Devices, a company I first covered in its “two guys in a garage” stage approximately ten years ago. This resulted in Logitech’s Squeezebox line of devices, which allow Android and iOS devices to act as remote controls for any music service that supports Squeezebox hardware ranging from small WiFi radios to home stereo components — or you can use them without those apps, if you prefer the devices’ own controls and remotes.

All of these devices now play Spotify in the U.S. and Europe.

(History nugget: Slim Devices is the only company that ever asked me to remove a positive review because their manufacturing process couldn’t keep up with demand.)

Onkyo Network-Capable Receivers

Evolver.fm received word from Onkyo that it is offering a free firmware upgrade that adds Spotify support to “its 2011 network capable receivers beginning with the TX-NR609.” Longtime Onkyo spokesman Gordon Sell added, “Onkyo will also be introducing additional networked Spotify-ready products in the near future.”

This system does not use Apple AirPlay, and, in fact, does not require any smartphone at all. With Onkyo, Spotify lives natively within the receiver itself. You control it with the standard remote control and view the Spotify app on your television.

Sonos Digital Music Systems

Longtime digital-music-in-the-home pioneers Sonos offers full support for Spotify Premium and many other music services — and claims that unlike Apple AirPlay, it can stream to multiple rooms at the same time without creating the muddy sound caused by phase cancellation (it’s complicated, but basically, if you want to listen in a bunch of rooms at the same time, just like the millionaires do, Sonos is the way to go).

You can control Spotify-on-Sonos using your laptop, Android, iPhone, or Sonos’ own remote control. The company offers a wide range of excellent audio home networking gear from standalone speakers to home stereo components.

Note: Spotify also partners with television manufacturers and services and other hardware companies, so this list will likely expand. (In fact, the company wants to hire someone in Sweden to manage those relationships.)

Bonus for Hacker Types: We hear that if you run Servify, you can bust out Spotify on a Boxee Box too.