Portable Sound Laboratories has an interesting solution that will protect your electronics and give you good sound at the same time. It's called the iMainGo2, and it's a 9 oz., clamshell zippered case that will hold an iPhone or an iPod touch. There's a headphone compatible 3.5mm plug that connects the case to your device. The unit runs on 4 AAA batteries for about 30 hours. We have one on loan for review, and I've been testing it around the house for a few days.
How does it sound? Better than I expected. It had nice bright highs, which were especially audible on percussion like snare drums and triangles. The bass is good, but this is not a device to equal a much bigger speaker system with a subwoofer. Still, it's more than reasonable. The unit appears to use a bass reflex or ducted port design, and if you close your eyes and just listen, you would think you were listening to a bigger system.