We can help you better if we know a few things first. Ok so you gave the length and width of your room, but how high is the ceiling? Is the room sealed or open to other areas? What is your budget?
Of the 2 subs mentioned above I would say go for the BIC Acoustech PL-200... I own the Acoustech speakers but not subs.
The PL-200, Klipsch RW-12d, and the Energy S10.3 are all highly regarded budget subs at $300 or under.
Now if your budget is upped to the $500-$600 range then you can start getting into pretty good subs such as: Outlaw Audio LFM-1 Plus, Hsu VTF2 MK4, Rythmik FV12, Epik Legend and so on.