Ok, here's the long answer.
yeah make sure you get good speakers that are tuned to eachother. usually speakers from the same brand and specific models are tuned to eachother so it sounds more natural.
Speaking from experience as a former installer for Tweeter, this is not as important as the car audio companies will have you believe. I will say this conditionally, assuming that the speakers are properly EQ'ed. It is NOT important to match speakers front to back, so long as they are amped and equalized well. It is, however, important to pick a brand of subwoofer and stick with it, nothing sounds worse than the mess that occurs when you mix sub brands(or models for that matter).
In my own opinion the most important pieces of any sound system are the source unit and the amplifiers. Nothing ruins the sound of good speakers better like a crappy amp. Conversely, nothing will make crappy speakers sound better than a really good amp. Now, as far as actual brands, I always recommend JL Audio and Boston Acoustics, although your selection may vary from Region to Region(Connecticut is big on JL, Texans likes Lightning Audio, etc.)
A good starting point for any system, price wise, SPL wise and SQ wise for me is:
1. Midrange Speakers
I would suggest The VR line or better from JL Audio or the FX line or better for Boston Acoustics. This boils down to personal choice, as JL's tend to be somewhat warmer (more bass), and Boston's tend to be a little brighter (more treble).
2. Amplifier.
As I said before, Amps are really important to proper sound and staging of a system, someone who amps subs but not mids is only asking for a crappy sound. That being said, I love Xtant amplifiers. They tend to be bright, but are stable at nearly any load you want to run and put out a very clean, loud sound.
Another option would be JL Audio amps, which, like all JL products, tend to be warmer in sound, and down on output when compared to the Xtant amps. What the JL's do have over the Xtants (and most other car amps) is the R.I.P.S system, which allows the amp to run off a variety of voltages (11-14.5), as well as maintain peak output through a variety of ohm loads(1.5-4). This allows more flexibility than most amps because you don't have to figure out what kind of load the subs will show your amp.
3. Head Unit
I have two recommendations I make for head units, both of these brands give you good sound:
If features are most important, I would go with an Alpine deck.
If Sound Quality is important, I would go with an Eclipse Deck.
I personally have an Alpine 7878 that I simply adore.
4. Subs
You have to pick the sound you like. I can't do much help here, although I can always recommend the JL W7, because it's a goddamned beast.
My only other recommendation is to avoid Sony at all costs, be it the Xplod or Mobile ES line, I've seen nothing but false output claims and reliability problems with their stuff.
<center><img src="http://www.silentspic.com/images/sighost/bobimpact.gif"><br>
<a href="http://www.silentspic.com" target="_blank">Thanks, Slient Spic!</a></center>