Great sub-woofer from a KEF 5005.1 System. Silver in color, 10" cone, 250-watt built in amplifier.
I moved into a smaller apt and got a smaller sub that won't disturb anyone. I've have had this one for 6 months or so and it has been great. Lots of controls for the built in amp (gain, phase, crossover, etc) will work with one sub lead or with red and white RCAs. It can really kick. Plenty happy with it, but its a little much for my smaller room.
New at Amazon for $700:
http://www.amazon.com/gp/product/B000EWP6YY
There are a couple of cosmetic scuffs from moving, and new it had some sticker sloppily peeled off the back (see photo). Works perfectly.
I also have 3 of the matching sats from the 5.1 system with stands here too, I would consider a package deal.
$400 shipped (would consider an AR upper for trade though
Large pics:
Front
http://i26.tinypic.com/1zq38ub.jpg
Rear
http://i25.tinypic.com/2lktxk2.jpg
Bottom
http://i25.tinypic.com/25kmmj4.jpg
Front2:
http://i32.tinypic.com/2isjgy9.jpg