The days of keeping a library of tapes or CDs in your car are over. You walk around with an MP3 player, so why shouldn't you be able to use it in your car? Today's MP3 players can hold your entire music collection, so you don't have to decide which tunes to bring with you. Today's cars let you easily plug in an iPod or MP3 player and have full control over the device through voice command or the car's touch screen, and that's much safer than trying to manipulate the small controls on an MP3 player while barreling down the freeway. We've picked six cars that work particularly well with iPods and MP3 players.