Decent subwoofer is whatever you wan/are willing to spend for a quality sub. I would suggest for the best HT/gaming experience you go with one that has at least a 12" driver as anyting smaller lacks the volume to move enough air for great effects. A 10" driver works but lacks the real lower end rumble etc. that the 12" and larger drivers offer, at least from my experience. elemental Designs, SVS, Axiom EP350 and up are all good sources of excellent quality subs but they may be more than you are willing to spend.
