I personally love my pioneer head unit, it has a digital input for accessories, and have installed an IPod dock in my wife's explorer that is cool, because it digitally interfaces with the IPod and charges it at the same time, it isn't just an aux. jack. As such, you can change tracks on the IPod from the head unit, and it will also display track information on the OLED screen.
As far as speakers go, I was on a budget, but wanted quality, so I went with Clif Designs, they are a relatively unknown company (to me at least) but these things are awesome. Her SUV, being a Ford, had 6x8's and the Clif Design QX5768's are awesome, with tweeters that you can adjust directionally. I also got her a pair of Clif Designs CD109W's which are 10" subs that can handle 300 watts RMS each (600 watts peak). Overall, I turned her terrible factory, government work truck model Explorer into a machine that she loves to drive and sounds incredible, and all on a budget. The hardest part was finding an amp that would drive those subs AND was affordable.
**Edit**
To reiterate what mouettus previously mentioned, the EQ and crossover settings on the Pioneer make it an awesome choice as well. Using the High Pass Filter and Sub crossover settings on the head unit allowed me to not have to worry about getting an amp with crossovers and such, just use the amp for... amplification.