I've owned my '97 base for about 2 months now and put a new Sony head unit in about a month ago. I wanted to find a solution for rear speakers that wouldn't take too much (if any) altering of the car, and I think I nailed it.
I ordered flat rear speakers from eBay that arrived today and they sound excellent. The cabin is full of sound with lot's of strong bass tones. The speakers are only 3" thick and fit right behind my seats (this works for me since I'm 5'8").
I have nothing to do anyone that sells these speakers, just thought I'd share. I attached a copy of the eBay listing I purchased them from... Enjoy!