Well, they are and aren't.

The tweet and woofer run to a cross over.
Since the tweeter can't reproduce bass and
woofers aren't made to reproduce highs and mids
the cross over divides the signal and sends it to
the proper speakers.

As to what type, that is very subjective and is mostly
up to the person looking for the speakers.
The best way to find a speaker you like is to sample
the ones he is interested in and if possible mounted in
a simular vehicle.


Some makes:

High range.

A/D/S (www.directed.com)
Rainbow (hard to find,very few dealers in the US, expensive)
http://www.speedsound.com/caraudio.asp?pg=products&manuf=58

Focal (www.focal-america.com)
DLS (www.dis-america.com)
Dynaudio (www.dynaudioausa.com)
Image dynamics (www.imagedynamicsusa.com)
MB Quart (www.mbquart.com)
Morel (www.morelusa.com)

Mid range.

Alpine (www.alpine-usa.com)
Pioneer (www.pioneerelectronics.com)
Clarion (www.clarion.com)
Kenwood (www.kenwoodusa.com)
Sony (www.sony.com)
Planet audio (www.planetaudiousa.com)
Memphis audio. (www.memphiscaraudio.com)
JBL (www.jbl.com)
JL audio (www.jlaudio.com)


There are more but it would get to long.

Hope this helps somewhat?

Louis.