www.adireaudio.com - the site may look lame but these are some of the best subs around. Try www.caraudioforum.com for advice on audio components as well.

I put in my system over a year ago and have loved it. Got a panasonic head unit, an adire audio shiva (12" 675W sub), a set of cadence 6.5" components (120W each) up front, a US Acoustics 4x85W amp, and a 1cf sealed encloser from www.speakerhole.com

This was all for around $650 including tax and shipping.

I installed everything myself. Had to make custom wooden holder in place of the old plastic speake basket to install the front speakers, but they do not have any clearance problems with the windows.

Hope this helps.

P.S: The quality is great, I can turn it up to painful volumes and I have yet to hear it distort. I played Prodigy - Smack My Bitch up at pretty high volume to show my friend the system and when it was done he looked at me and said "my heart feels funny". I guess it's got some decent bass