Put me down as another one who picked up a $15 charger at Walmart dubbed "compatible with Motorola." On a note about charging and cord differences though, I have noticed a few things. First, my cheapie car charger from Walmart does work, but it is somewhat slow to charge. It is faster than USB from a computer, but slower than a wall charge. Also, I have a 1FT generic USB extender that when used, also charges my droid much more slowly than any of the aforementioned methods.
I would recommend going with a Motorola branded charger, as the specifications are fit to the model of phone and the battery. However, if you need to charge in a pinch like on a road trip there certainly isn't anything wrong with the $15 Wal-Mart option. It may come at the cost of your battery however over time, but even those are only $30