ZyDistro via eBay offers the Dual Port USB Car Charger in six colors (Black pictured) for $2.95 with free shipping. Although we saw it for a buck less last week, that's the lowest total price we could find today by $4. It features an LED charging indicator, built-in charging circuitry, and fits any 12-volt accessories.
Note that you have to choose a cell phone or tablet to add the charger to cart. (Charger specs are the same regardless of what you choose.)