I saw this in this months Moble Entertainment mag (ME). Its Earthquake's SWS 10 in subwoofer.
Its mounting depth is only 3 inches deep. So you could mount it in your side pannels or for all of you that are making wrap around seating for your SAN's and you need shallow woofers or for the crazy people with woofers on the tower's This might be a good option for you. I also see Audiobahn is making shallow woofers. I havent heard these but on pape they looked nice.
Just over $300 each