Well I just got my 10000k bonus from the army and I'm putting the majority away in the bank. For now I just want to put speaker and an aux connection in. What brands of speaker and what are a few ideas about how to to make the truck stereo sound good without putting a brand new head unit in.

 

I have the Infinity Kappa, 5x7 components in the front doors, and 6" components in the rear doors (tweeters in the b pillars) with a Kappa 5.1 channel amp. It sounds great, but a lot will depend on what you want, I'm old and want high quality sound, and enough volume so I don't have to listen to the hip/hop from the car next to me. However if you want the loud hip/hop you probably want a different setup.

I have a pioneer navi head unit, but no reason you couldn't keep your head unit if you wanted to.