First, there was radio. Then there were 8 tracks. Then there were cassette decks. Then there were CDs. Now it's all MP3s. Which means that we're actually back to radio.
I bought an attachment for my iPod yesterday to allow it to play music through my car stereo. It turns out that it can actually play music through any radio - which should've come as no surprise, but I hadn't thought it through that far. It certainly saves me from buying separate iPod speakers.