You can use any 5V usb charger that outputs more than 500 mA. I'd stay away from $2 ebay chargers though.
I bought this charger here.
http://www.amazon.com...
I just use apple supplied chargers, nothing more. Some of the cheap knock offs could cause issues.
Will using a different charger effect your battery on iPhone?
Will using a different charger effect your battery on iPhone?