Agree with Nate's suggestion -2 x L12's or F12s depending on your budget. You could also start with one and add a second later. I prefer sealed although from what I've read, with Rythmik subs the ported perform very well with music as well.

Depending on your space/placement options, you may also want to look at the L22 or E15. The E15 is only a bit bigger than the F12. I use 2 E15's in my room (16x12x11, but opens to Den (~22x20) to left and Dining Room (16x12) behind, fills the space nicely.