Pretty much any "name-brand" speaker with a poly cone will work for you. Since you're not getting nuts, you don't have to get nuts buying speakers - although I will suggest you leave room for an upgrade later.
I've got Sony Xplods in one rig, JVC polycones in another, and Polk Audio 5.25" and Rockford 6x9's in a third. No amps - I've only got an amp in my 88 to drive the sub. All sound very good, although I've also long since gotten rid of the OEMR stereo (I need a front panel input as well.)
You should be able to get decent speakers all the way around for about $100 if you stay with stock size (usually 5.25" round,) or $150 if you go a little larger in the back (you can stick a shallow 6x9 in the liftgate, with some modification. I've got that done to three of my rigs - took about an hour with a Dremel to modify the fibreglas liftgate, but it was worth it.) Going with a larger cone in the back will allow you to put out some more low-end, which should fill your music neatly.
As you've already figured out, an amp for the four speakers isn't really necessary (and if I did run one, I'd be more interested in signal/noise ratios and filtering capability than in pure power output - that's just me.) Going with speakers with 100W power handling or thereabouts should be no trouble - even most aftermarket decks only put out about 50W per channel/speaker wire set. You can always drive a speaker with LOWER power - it's when you use MORE power that it becomes a problem (voice coil failure and cone excursion intereference come to mind.)
Since you don't say what year, it's hard to say for certain what size your speakers are now - but I'm almost willing to bet they're 5.25" round cones. If you'd like to know more, you can do a lookup at Crutchfield (
www.crutchfield.com,) and if you'd like to make sure you weren't modded before you got the vehicle, pull the inner liftgate panel and the door panels. I see no reason, really, to mod the door shells to take a larger speaker, but the liftgate mod is probably fairly common - and visually inspecting everything is the best way to be sure.
5-90
