The OontZ Ultra-Portable Wireless Bluetooth Speaker by Cambridge SoundWorks
I am a golf professional and bought a couple of these, 1 as a gift for a student, and 1 for me. At our club, we are all addicted to good music and cannot play a round of golf without it ( it makes a long round of golf that much better).  I had a chance to use it on Monday, and in a word it is AWESOME.  I was truly blown away by not only how loud it is, but the quality of the speaker.  I also had a jambox (that I lost last year) and it doesn't compare - not as loud and I had a big issue with the battery life