120W is not enough if you want really deep and loud bass. Look for something home audio and mid range, at least 200W.
Amazon.com: M-Audio SBX10 240-Watt Professional Active Subwoofer: Musical Instruments
That is my choice for a really good mid range sub. Check Ebay for deals, I got a nice deal on a 100W sub new in the box for $60 to my door a few months back.