Car CD changers

Sony Xplod CDX-GT630UI
Specs: Auxiliary input, USB

Kenwood 50W x 4 MOSFET Apple iPod /Satellite Radio/HD Radio-Ready CD Deck

Dual XDV8125
Specs: Audio line-out, Composite video/audio input, Composite video output, Component video input, Navigation system input

Clarion CMD4 - radio / CD player
Specs: Radio / CD player, Radio tuner, CD player, Audio line-in, Audio line-out, System components control bus, Remote control

Kenwood KDC-138
Specs: Radio / CD player, Audio line-in, Audio line-out

Sony CDX-GT520
The Sony CDX-GT520 is a decent option for those wanting a reasonably priced stereo to play disc-based audio. While it does support HD Radio, it requires the connection of a clunky add-on module, which is almost more trouble than it's worth.
Specs: Radio / CD / MP3 player, Radio tuner, CD / MP3 player, Audio line-in, Audio line-out, Subwoofer output, System components control bus

Kenwood KDC-X890
The Kenwood KDC X890 is a capable head unit that supports a broad range of audio formats. Voice indexing helps counteract awkward manual file selection, although the system's claims that it measures car performance are dubious.
Specs: Radio / CD / MP3 player, Radio tuner, CD / MP3 player, USB, Audio line-in, Subwoofer output, Rear channel output, Front channel output

Kenwood KDCMP208 MP3/WMA/CD Receiver
Specs: Radio / CD / MP3 player, Radio tuner, CD / MP3 player, Audio line-in, Audio line-out

JVC KD G140 - radio / CD player
Specs: Radio / CD player, Radio tuner, CD player, Audio line-in, Audio output

Kenwood KDC MP638U - radio / CD / MP3 player / digital player
Specs: Radio / CD / MP3 player / digital player, Radio tuner, CD / MP3 player, Rear channel output, Front channel output, Audio line-out, Audio line-in, USB, System components control bus

Kenwood 50W x 4 iPod /Satellite/HD Radio-Ready DVD/GPS Receiver with 7" Monitor

Pioneer DEH P47DH - radio / CD player
Specs: Radio / CD player, Radio tuner, CD player, Speakers output, Audio line-out, System components control bus

Clarion ProAudio DRZ9255 - radio / CD player
Specs: Radio / CD player, Radio tuner, CD player, Audio line-in, SPDIF input, SPDIF output, Audio line-out, Ce NET

Clarion DXZ 665MP - radio / CD / MP3 player
Specs: Radio / CD / MP3 player, Radio tuner, CD / MP3 player, Audio line-out, Audio line-in, System components control bus

Sony CDX-GT120
Specs: Radio / CD player, Radio tuner, CD player, Audio line-in, Audio line-out

Kenwood KDC 1032 - radio / CD player
Specs: Radio / CD player, Radio tuner, CD player, Audio line-out

Kenwood Excelon KDC-X790 CD/MP3 Player

Kenwood DPX 301 - radio / CD / MP3 player
Specs: Radio / CD / MP3 player, Radio tuner, CD / MP3 player, Audio line-in, Audio line-out, System components control bus

Boss 745BA Car Audio Player

Pioneer DEH P77DH - radio / CD player
Specs: Radio / CD player, Radio tuner, CD player, Audio line-out, Subwoofer output, Speakers output, System components control bus

Sanyo FXCD-550 - radio / CD / cassette player
Specs: Radio / CD / cassette player, Radio tuner, CD player, Audio line-out

Sony 10-Disc CD/CD-R/RW Changer with Wired Remote
Specs: CD changer, None, CD changer, System components control bus, Audio line-out