Buy.com offers the Miccus ChargeBlock XL Battery Charger for Apple iPhone and iPod, model no. CBFI-15, for $19.99 with free shipping. That's tied with our August mention and the lowest total price we could find by $5. This 1,500mAh external battery powers and recharges your iPhone or iPod using the 30-pin dock connector.
Update: OrderBorder offers it for $19.75 with the above shipping.