I picked up one of these MP3 transmitters from DealExtreme:

http://www.dealextreme.com/details.dx/sku.10130

I've been using mine for a few days now and I tried the SD card and using the included headphone jack cable hooked up to my Zune.


Pros:
- The FM signal is quite strong and I have absolutely no problems getting a signal from this device. There isn't any kind of "FCC-compliant" writing on the device. Since it’s coming from Hong Kong, I think maybe this is why the FM signal is so strong.

- Playing MP3's from an SD card is easy.

- Can easily transfer from vehicle to vehicle.


- Remote control is handy.


Cons:

- There is no instruction manual, just some simple pictures/diagrams.

- The headphone jack cable that came with the system does not work properly. I have to jiggle it to get it to work.

- Haven’t figured out if it supports playlists yet.

- Took almost 17 days between order and delivery.

The unit also has a USB connection that I have not tried yet. The sound quality is acceptable for me. I would give it a 6 out of 10. Overall though, I really like this device. From my experience so far, this is the best $10 solution for having MP3's in my roadster.

 

I tried one and took it back the next day. It used SD and usb. They were still $50 back then. Sound quality was really bad no matter what channel I used on the radio and had to turn up the volume really loud on the radio.

James