I have this
http://www.dealextreme.com/details.dx/sku.10130
It's only $6.50 and works great. It will play mp3 off a SD card or USB thumb drive. There is an included cable that lets you plug into the TP2 headphone jack. It's short so I gave you a link for a cheap extender. These players are great and they are VERY STRONG. Only thing is sometimes you get a bad one and you need to email them and they will send you a new one. This thing is so strong that when I follow my wife in a different car and tune into the station it is broadcasting. I can actually hear what she is listening to pretty clearly. I been using this for Slacker and Kinoma Free Play and it works great.
Also they ship from Hong Kong so it takes like 2-3 weeks to get it.
For Dual charging get this.
http://cgi.ebay.com/2-Way-Splitter-l...item2c5300b9f7
For an extension for the 3.5mm jack get this.
http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT