I've been looking at one of these (
Welcome to Belkin - TuneCast II Mobile FM Transmitter) for a while with some trepidation: most say that the quality of the FM broadcast isn't that great. But now I have one and I can say: That's not what I found. I now have a 1GB SD card with various podCasts downloaded and plug my TuneCast II into my iPaq 1940 and can now listen to what I want to when driving to and from clients. I go to client office's only sporadically (most I can connect to remotely) and work from home but having this on my PDA, which is my main source of information, makes it an awesome tool.
Great frequency (88.1 to 107.9) and powers on and off automatically and runs on 2 AAA betteries. (I'll find out how long these really work)
Maybe now I'll start PodCasting my own stuff.