Just bought a '05 Hyundai Sonata. Came with the factory CD/cassette
stereo.

I've been using the cassette adaptor to listen to my iPod, and it
sounds fine, but what I'd really like is direct input for better sound.
I understand that some new car stereos have an auxiliiary input in the
rear of the unit. Instead of ripping the head unit out of this brand
new car to check, I ask: Does anyone know if there's one back there?

I'd check with the dealer, but I'm sure they wouldn't know what I'm
talking about.