MTX, Soundstream, Precision Power (and the list goes on) all makes nice sub amps.
You really need to decide what driver you will use before you select the amp. The are so many amp/sub configurations available, and you need to select them to maximize the performace of the amp. I say this not only to gain output, but you might also save $$$ on the amp.
If you go with the DSQ, a nice 2 channel amp that will run 4 ohms mono would work great. I would recommend:
http://www.millionbuy.com/sosrub5002.html
It is the Soundstream Rubicon 500.2. It is a nice amp for $169!!!!!
Search the web for prefab boxes. There are many available. Sometimes it is about the same price just to grab one from Circuit City, Best Buy, or a local shop, as shipping is expensive. You can also find ABS plastic enclosures made to fit the vehicle, but make sure the sub is goig to fit. . .
I see you are from Austin. . . are you a student at t.u.?
Gig'em Aggies!!!
Brian