In article ,
says...

Hi, The quality of my current headphone jack-to-cassette adapter is poor,
and so I am looking for a car radio that has a line-in, but either I am
not searching for the right phrases, or such a thing doesn't exist. I am
wanting to plug in any such device - walkman, minidisc, portable MP3
player, etc - so that I can listen to it through the car speakers.

Look for units that support Line In, AUX in, or EXT/Audio in.
As has been said normaly it is a line that uses the CD changer input.
Blaupunkt is a £10 lead, other like like Sony charge from £50-100
depending on what you want (the top model has two AUX ins, a USB AUX in
for laptops and digital players, plus a cd changer pass through)

Goodmans are the only budget brand you regularly see with line in
sockets but they tend to be on the front.
Some Pioneer and Alpines have them on the back but are pricey.
Nakamichi are very expensive, but both the standalone CD Headunits have
line in with RCA jacks on the back but look at £400+ for a basic
Nakamichi CD Headunit.
--
The poster formerly known as Skodapilot.
http://www.bouncing-czechs.com