I suppose by now, every CDT/Rainbow dealer on the board has already gotten to you. I'd strongly urge you to listen to do some listening to different speakers and see what you like before you buy. Check with your local shops as well. The manufacturers will usually be happy to steer you toward a shop in your area where you can do some listening. Buying speakers is like buying clothes. Everyone has different tastes and what suits one, may not suit another. I'm sure you try on clothes before you buy them, you ought to do the same with speakers.
Besides the current boners on this board, you might also want to check out these options:
http://www.ozaudio.com
http://www.arcaudio.com
http://www.zapco.com
http://www.bostonacoustics.com
http://www.jlaudio.com
http://www.dls.se
http://www.morelhifi.com
http://www.audiotec-fischer.com/englisch/helix_englisch/helixstart.html
http://www.adst.com
http://www.focal-america.com/
http://www.canton.de/en-serie-car.htm
http://www.mbquart.com/en/
There are lots and lots of good options out there in your price range. Until you know what kind of sound you're looking for in a speaker, I wouldn't buy anything. That doesn't mean you HAVE to buy what's around you, but if I know that, for example, you like bright highs, I'd recommend MB Quart, Boston Acoustics, Focal or Canton. If you like warmer highs, then I know Oz, a/d/s, Morel or Helix are a better fit. You have to develop the ear for what you want from a speaker.
The reason many recommend against rear-fill is that they're behind you and they can make imaging more difficult. Think of going to a concert: You don't turn your back on the performers do you? Most people want the sound in front of them. Having speakers behind you can draw the sound behind you. This is especially problematic with subwoofers, as most of us mount the subs in the rear. Giving the illusion that the sound is up front gets harder with rear-fill. Also, rear fill can cause sound cancellation, particularly with the highs.
However, with more people installing surround sound in cars, rear-fill is becoming more important. It's a call you'll have to make, but I think the point is that you should put the majority of your focus on the fronts. There are plenty of cheaper options that'll do fine for rear-fill. Don't spend a lot of money there. I'd rather have $300 in my fronts and $100 in my rear-fill than $200 all around.
Hope that helps.
