Newegg offers the Polk Audio 300-watt 12" Powered Subwoofer in Black, model no. PSW505, for $179.99. Redeem this $30 mail-in rebate to cut the price to $149.99. With free shipping, that's the lowest total price we could find by $30, although we saw it for $6 less on Cyber Monday. It features a frequency response of 23Hz to 160Hz, magnetic shielding, phase switch, and adjustable crossover. Rebate expires December 27.