Check out this LiIon/LiPoly 3.7/4.2V battery charger based on MCP73833. It takes a USB mini-B for connection to any USB wall adapter or computer. The fast-charge current is 500mA by default but it is adjustable from 100mA up to 1000mA using a through-hole resistor on board.
Great for DIY projects, includes 3 indicator LEDs – for power, charging status and when charging is complete. Recommended to use Adafruit Lipoly batteries. Also includes JST connector for battery and load system so that you can keep the battery connected to the charger and pass the power through.
Buy USB LiIon/LiPoly charger from Pakronics: