I just bought an iRiver AFT-100 FM Transmitter to complement my new favourite toy. I had heard bad things about FM transmitters in big cities, but so far I'm having a great deal of success playing my MP3 player on 94.3.
Many moons ago I dreamt about a day when I could hear virtually anything I wanted to in my car with the press of a button. Today, I have 5 GB of my favourite high quality MP3s at my disposal while I commute. I'm a very, very happy man.