Newegg offers the refurbished Logitech Z506 5.1-Channel Surround Sound Speaker System, model no. 980-000430, for $54.99. Coupon code "EMCWPGP78" cuts it to $39.99. With free shipping, that's tied with last month's refurb mention and $30 under the lowest total price we could find for a new unit today. Features include 75 watts RMS of total power, a down-firing subwoofer, 45Hz to 20kHz frequency response, and 3.5mm audio input.
A 90-day warranty applies, although it's unclear who backs it.