One of the first things I did was get rid of the factory stereo and speakers. I installed a Blaupunkt Seattle MP/CD reciever.
I also replaced the speakers with Infinity 6.5 components. I had to mount the crossovers under the drivers seat.
I bought an Alpine MRV F302 amp off Ebay. It's 30W X 4 at 12V. It's a perfect fit under the passengers seat. I was a little worried that it wouldn't be enough power but it's more than enough for a set of components and a small sub.
I have a MTX 8 inch subwoofer in a Q logic box. It's enough bass for me for now. I might upgrade in the future.
I added a XM Roady that is hardwired into the back of my reciever. I also added a Blaupunkt CD changer which is mounted behind the drivers seat. I also Dynamatted most of the interior.