Ultimate Ears UE Roll
I am resurrecting this thread because of a great speaker that I have been using for the past week. A couple of guys I play with have them and I was impressed so I picked one up for myself.
Here is the manufacturer's link, with video.
http://www.ultimateears.com/en-us/roll
Here's the Amazon link to the various colors, etc. They run $99
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=ue+roll
I am not a big fan of tiny speakers, and generally feel bluetooth + tiny speaker + mp3 setups blow, but this thing actually works and sounds amazing for a single speaker at this price point. It's also water and dirt proof (as in you could take it into water and can wash it in the sink, apparently), holds a 9+ hour charge on its internal batteries (charged through USB on a standard mini cable), and is more than loud enough without having the boxy / overly boomy tone typically associated with the Beats products and so many that are trying to copy that sound profile. It's still a single speaker, but as somebody that listens to music constantly, I cannot hate on the sound from this thing.
You can run any of your sound apps on your phone to drive the speaker, and UE has a free app that you can use to remotely control all of the speaker functions remotely, including turning it on and off, which could be handy. I haven't used it yet, but my friends that use the same speaker seem to like the app.
The attachment system for your bag is a bit tenuous if you are going to have it bouncing around on your pack, but I just ran a zip tie through the provided elastic cords on the back and it hasn't come loose since.
Here is the speaker on my bag. The + / - on the front are handy volume controls.
At any rate, I have nothing to do with the company that makes these or anything, but this is a great bluetooth speaker for background tunes on the course. I have been really impressed with it.