Sweex has a great set of USB speakers for under $40USD. The SP007 speaker set are perfect compliments to your laptop or PC, with quick and easy install, no external power supply and use of USB port for power. The SP007 has an internal amplifier for improved sound. Speakers are also magentically shielded and are 120 Watt. Sweex also offers speakers at 180 Watt and 200 Watt specifications.
