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Buy.com has the Logitech X-540 Speaker System for $71.24, the lowest we've seen not involving a rebate. This features four satellite speakers, a center channel, and a 140-watt subwoofer. It's well reviewed, receiving 4.5 out of 5 from over 60 reviewers. Shipping is free and there is no sales tax (except CA, MA, MD, TN).