2-10" Polk DX or Boston Pro series... 2 of the most acurate and powerful subwoofers ive ever heard... (besides the Sunfire true subwoofer, home sub)

Also a good choice are the Alpine type-R subs... awesome!

just a couple suggestions... all of them use TINY sealed boxes... 0.5-0.75 cubic feet per sub! and handle a TON of power... you'll get plenty of clean, deep and loud (if you like) bass!