JBL ES250PBK High-Performance 12-Inch Powered Subwoofer
The ES250P is the perfect subwoofer for a medium sized home theater or den: it's affordable, looks good, and sounds like most people expect a subwoofer to sound. It has a 12-inch downward-firing woofer puts out plenty of tight, deep bass that leans slightly toward the midbass rather than deepest notes, but does reach into subbass while remaining fairly tight, meaning that rap, pop, and electronic music will get plenty of oomph but won't keep the neighbors awake as long as the volume is kept at reasonable levels; comparable models from Bose or Klisch, like the SW100, focus more on mid bass and tend to sound overly loud and a bit boomier. Make no mistake: the JBL can rattle walls, and will if you crank the volume, but it can also be kept relatively tame.
Please keep in mind that this is an entry level subwoofer; if you are expecting genuine room lock in anything bigger than an average bedroom, or want to use it outdoors, you should expect to spend more money. Some users have reported blown fuses when the unit is pushed to its limits, but JBL has reportedly included a higher quality resistor in newer units, so defects shouldn't be a problem as long as you're buying new. At the price, this is a great subwoofer, and as long as you don't push it to its limits constantly, you should be very satisfied with its performance.