US Acoustics USX-4065 Car Amp

The US Acoustics USX4065 gives you the most for your money. It is a 4 channel amp with built in electronic crossovers. The built in 24 db/octave low pass crossover sounds much better than amps with more shallow crossovers. It helps keep your sub from sounding "klunky". It is a good value, but not "cheap". The finish and quality are good. As a bonus the amplifier is made in the USA.
Installation is easy, although it would be nice if all the controls, inputs and outputs were on the same side. If you are mounting it near an edge, it can be hard to adjust the crossover or plug in wires. I bought mine from Crutchfield for $199. I don't think it would be worth the extra money to get the higher powered version unless you were going to drive all subs. The amplifier is bridgeable, so it can power two main speakers as well as a subwoofer.