We just checked out Soundmatters' FoxLo, a palm-sized subwoofer that can connect to the company's FoxL portable Bluetooth speaker, or other portable speaker systems with pass-through output. Unfortunately, to use the woofer you'll have to plug it in directly to your laptop, which sort of defeats the purpose of using portable wireless speakers. Still, it's fairly small and light — weighing in at only 23 ounces — and should be due out in Spring 2012 for $149.