Car CD changers

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.

Kenwood Excelon KDC-X790 CD/MP3 Player

Pioneer CDX FM1287 - CD changer
Specs: CD changer, None, CD changer

Kenwood KDC C717 - CD changer
Specs: CD changer, CD changer, System components control bus

Panasonic CQ C1121U - radio / CD player
Specs: Radio / CD player, Radio tuner, CD player, Rear channel output, Front channel output

Panasonic CQ C7103U - radio / CD / MP3 player
Specs: Radio / CD / MP3 player, Radio tuner, CD / MP3 player, Front channel output, Rear channel output

Panasonic CQ C3303U - radio / CD / MP3 player
Specs: Radio / CD / MP3 player, Radio tuner, CD / MP3 player, Front channel output, Rear channel output

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

Panasonic CQ C1333U - radio / CD / MP3 player
Specs: Radio / CD / MP3 player, Radio tuner, CD / MP3 player, Front channel output, Rear channel output, Audio line-in