My suggestion would be to get a Nakamichi CD-400 head unit (simple, stock-looking, and great sound - check eBay) and a couple pair of
Crystal CXe-570 coaxials (which have outboard crossovers).
Add a small sub/amp combo later on if you find the bottom end lacking (the smaller cones on full-range speakers can only move so much air). Not all people find a sub necessary, tho. A single 8" free-air sub mounted to the bottom of the rear deck will usually do the trick for people wavering on the sub vs. no-sub issue.
Outboard amps for the coaxials will also "liven" them up, so they'll sound better at higher volumes and have some extra mid-bass punch. It's not a necessity, but it'll make a very nice improvement over just the head unit power.
BTW, don't forget to bypass the factory amp (if so equipped). It'll cripple the aftermarket head unit if it's not bypassed.
