Good subwoofers for music?

i want to get a subwoofer for music, not for movies or anything... and its gonna be in my bedroom which is 13 by 13. also, i dont want so buy a vandersteen or whatever they are cause its like $1,300. i just want a general idea on what subwoofers are good for music, like a polk audio i listen to rap, as in tech n9ne, tupac, dr dre, nwa, ice cube, and mostly older rap.. thanks for helping.