Got to know this really cheap external battery charger for iPhone 3G from Hardware Zone Forums. The seller, free-4-flying, is based in Hong Kong. Once in a while he will have a sale on that. The cheapest I saw is US$6.99 but unfortunately when I bought that time it is US$8.48 (S$11.87). The price stated includes shipping which makes it real cheap!
I bought it on the 18th September 2009 and it was shipped on the next day on 19th September 2009. Took 17 days to reach me, arrived in my mailbox yesterday on the 6th October 2009. This is technically the first item I purchased from eBay. The very first item I bought is the Apple Care for my MacBook Pro =D