I found that the weak link was in the OE speakers on my 99'. New 3-way Sony's made a huge difference while keeping the stock (Clarion) head unit. I then also added a Kenwood powered sub woofer, an OE CD changer under the passenger seat and Sirius Sat radio. Couldn't be happier!
Cruchfield is a good place to see what fits. Shop around for the best pricing though.
Crutchfield: Car Audio, Home Theater, Speakers, LCD TV, Plasma TV
