Here's an alternative idea: get a pair of subs, rather than just one, as a pair will provide lots more "oomph". Further, if placed properly, a pair of subs will load the room much better than one.
Outlaw Audio has a good sub (the LFM-1) that was designed for them by Hsu, and Outlaw currently has a special deal on a pair of the LFM-1 subs for $999 (they also provide a 30-day money-back trial). For more info, go to the following link:
http://www.outlawaudio.com/products/lfm1.html
Outlaw also has a smaller sub, the LFM-2, and you can get a pair of them for $549. See their web site for more info.
Outlaw's web site re-publishes a number of reviews of the LFM-1 sub. Here are links to three of the better reviews:
www.audioholics.com/productreviews/loudspeakers/SVS_subsPB2-ISD_OutlawLFM-1_1.php
www.hometheatersound.com/equipment/outlaw_lfm1.htm
www.hometheaterhifi.com/volume_11_2/outlaw-lfm1-subwoofer-4-2004.html