Macworld has a nice little review of 9 rugged Bluetooth speakers designed for outdoor use
here. In summary:
* Braven BRV-1 and Philips's Shoqbox offer great combination of ruggedness, portability and sound quality with Scoosche's Boombottle being a good option for cyclists
* EcoXBT is a great option for people on the water a lot
* TDK's A33 and Nyne's NB-250 are excellent choices for car camping or patios being a bit bigger and heavier than some of the others but offering the best sound quality
Most of the units tested have a USB or 3.5mm audio jack if you don't want to go the Bluetooth route.