I'm using the car adapter meant for the Nintendo DS. It came with a slick carrying case and the USB adapter for like $11 shipped (via eBay). The fantastic thing about this particular one is that the part that plugs into the cigarette lighter just has a normal USB slot and is not hard wired to the cable.

i.e. if I wanted to charge something that uses just regular USB (iPod) to charge with all I have to do is swap from my USB->Mini USB cable (used to charge the Mogul) to the cable supplied with my other regular USB based device. IMO, it is an ideal setup - cheap, flexible and gets the job done! I would probably have paid more for this type of car adapter than just a regular mini usb->car that's all one piece just for the flexibility alone.