For tunes on the go, the Eton Rukus Solar stereo uses an eternal power source: the sun. Measuring about 12 x 8 in. and weighing just under 5 lbs., it plays music over an A2DP Bluetooth wireless connection from any tablet or smartphone.
There's a sturdy carrying handle, a USB port for charging your phone, an auxiliary input for any MP3 player, a crisp e-ink display and large solar panels on one side. The stereo costs $150, but you'll rarely need to buy batteries. (On cloudy days, you can use four AA backups.)
In my tests, throaty vocals from Anya Marina sounded decent, without a heavy bass, and the Rukus lasted all day at the beach.