This week I purchased a Nokia DC-20 Universal Dual USB Car Charger as I needed a new one with a higher output (1000mA). After looking around this one had the specs I was looking for and the price too (£10 on Amazon UK). It has two ports that can both give the full output so you can charge any two USB powered gadgets at the same time.
There's not much you can say about a car charger other than it works well, is well presented and very good value! I would strongly recommend it to anyone that needs one, not just Nokia users.
Nokia's product link for the DC-20: http://europe.nokia.com/find-products/accessories/car-and-navigation/car-chargers/nokia-dual-usb-car-charger-dc-20