Our washes are 50's themed so I use an ipod nano at each site that's set up to repeat a shuffled playlist of 50's rock & rockabilly, 24/7. I use a line-out from the Nano to a Denon amp and a power adapter powers the Nano through the dock connection.
The Denon amp is connected to an analog 24hr timer so it shuts off late at night but the Nano's continue to play all the time! That way, when the amp activates by the timer in the am, the source music is already playing. I don't touch a thing except for changing to an xmas playlist during the holidays.
No skipping CD's, no commercials and about 250 randomized songs for variety.
I tried a few of the apple docks but I had problems with the ipod's stopping play-back after a few days.
I find that the tunes put a smile on washers faces and lightens the mood dramatically. I use standard 8 inch in-ceiling flush speakers.