I plug my iPod into an old Yamaha receiver and a newer JVC desktop stereo. Both of them just take line inputs. I'm not really a car audio guy, but I figure a line level signal is a line level signal (excepting head units that have higher-level outs to minimize noise for competition stereos).
If you're willing to have it set up so the iPod isn't charged by the connector, I'd just plug in the headphone jack and call it a day.
