take a look at the vmps line of subs(passive )i have the vmps large sub and it is great.if you buy from a authorised dealer you can save a few bucks also.external amps are nice because you can upgrade to a bigger one at some point.
i looked for months for a sub till i found this one,also you might take a look at avs fourum theres a thread about people who gave up svs for vmps.