As usual, Chris is WAY ahead of me on this.

I've been using a Motorola T505 to stream music in my car from my Droid for a while. I don't know if it is the BT part or the broadcast to FM part, but I think the quality generally sucks.

It is a very convenient and inexpensive device, though. Amazing, really. Allows me to use the car speakers for phone conversations.
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