Polk makes a good sub. I've always liked the dB and dX series subs. The current Polk MOMO's, while good subs by all accounts, are outrageously priced.
I'd suggest taking a look at the Image Dynamics IDQ12V.2 D2 which would mate very well with your amp and only require .65ft^3. They run for 'bout $150.
The Dayton DSQ would definately be a good choice for a single 12" sub.