DC/DC Booster to 5v 500ma?
Pretty much most boost converters do what you want. Anything that uses 1 or 2 AA for a usb charger have this.

The MintyBoost is a popular (and fully detailed) diy kit for boosting 2 NiMH or Alkaline to 5v at 500mA.

It is based on the dip LT1302 with the usual passive components needed.