Google Chromecast Audio: Stream your favorite music with Google Chromecast Audio. Simply plug into your speaker's auxiliary input and connect to your Wi-Fi network. Then just tap the Cast button from your favorite apps on your phone, tablet or computer to cast songs, radio stations and podcasts to your speaker.
With some setup involved with the app and connecting to the device, once that was taken care of I was able to access my music library that I stored in Google's Play Music app (psst, they allow you free uploading of 40,000 songs, free). It has been amazing turning my older high quality speakers into a great streaming system.
Expect good sound quality but not great. For $35, its worth it. The Marvell DAC inside the device is a good one you aren't getting a Sabre, Wolfson or Burr-Brown. You get what you pay for.