As far as speakers I personally like the Infiniti speakers and Im sure other people here would tell you the same. The sound very clear and crisp and have good power to them, you can pick up a good set of Infiniti Reference for about $90/pair.

An amp would make it sound much better, clearer, and louder. As far as amps go everyone has their brand preference but I suggest getting a 4-channel amp, I have MTX amps and have never had any problems with them and they are somewhat cheap.