I will agree that Alpine subs are UNDERrated, especially the type R. A whole lot of bang for your buck with that sub, and they can utilize a smaller encloser better than many.
BigTBones, if you listen to music and not a tuned frequency level, why in the world would you want a ported box. Dont get me wrong, Ive had them and they do have their place but SPL is the only one I can think of.
Evan, I would stay away from the lower end MTX sub's but if you do go that route stay with a sealed enclosure. I had a pair of 6,000's (2-12's) and they sounded pretty good. You also might want to check out Infinity, really good stuff for not a whole lot of cash...
1997 Kawasaki Bayou 220
2004 Yamaha YFZ450
1985 Honda 250ES
1982 Honda 185s For Sale