Here's what I put under the drivers seat of my 05 S non RF:

Linky: Phoenix Gold Octane R4.0:2 400 watt bridgable amp

It was recommended to me by a coworker who used to be a pro installer before he became a computer geek (my requirement was a decent amp that wasn't too expensive). It's driving a Bazooka ELW 1014 10” with plenty of power to spare.

Here's some pics of the install so you can see how an amp that size fits.

Linky: Install pics

Edit: Oops the link above (where I bought it from) is out of date. Here's an active auction for the same thing, different seller:
Linky: Active auction for the same thing