The best I've had so far is the
Griffin 9749-P JBLK PowerJolt Auto Charger for iPod (Black). It works beautifully with the 3G or 3GS iPhones. I've bought 3 chargers in the past that didn't have the right voltage so you have to be very careful which one you choose, even if it says it works with the iPhone. You have to make sure it works with your model iPhone. It also comes with an extra USB cable, which is nice. You don't have to buy it from the link to Amazon if you don't want to. Do a search and see if you can find it somewhere else, possibly cheaper.
https://www.amazon.com/gp/product/B0...ss_T15_product