Amazon has this Apple iPhone USB Sync and Charging Cable for just $0.90 + free shipping right now. You can’t find these anywhere for less than $20 retail.
At this price, it couldn’t hurt to buy one just to have an extra lying around. You know how those cables always seem to go missing…
Reading the reviews of this product on Amazon, I would not recommend this product. People complained about them not working and causing the iphones to overheat. I am also not sure how they can not charge shipping since it is coming from Hong-Kong? Seems suspicious to me!