I saw one of these on New Year's eve, and was amazed by the sound quality.  The X-Mini II Capsule Speaker
 will fit in your pocket, charges via USB, and plugs into any music device with a 3.5mm headphone jack. The capsule twists open (shown) to reveal an accordion-like mid-section that helps provide sub-woofer type bass.  No, it doesn't compare to the Altec Lansing iM600 I bought 3 years ago, but for $30 and its tiny size, the  sound is remarkable — and you can connect multiple capsules together daisy-chain style for truly room-filling sound.  Buy it for $29.98 with free shipping from Amazon.com.