Not happy with the $84.95 iPhone battery replacement from Apple?
iPodJuice is now offering a 1400 mAh replacement battery for the iPhone which claims to be comparable to the original iPhone battery.
Our 1400 mAh lithium-ion polymer battery is the same strength as the one that came with your 8GB iPhone. This robust battery is 100 percent compatible with your iPhone and is guaranteed to last for ten years from the date of purchase.
The battery itself only costs $25 at this time, but "is very difficult for the average consumer to replace" according to iPodJuice. They offer install/shipping options that range from $20-$70. If you are technically inclined, you can buy the battery alone and have a go at it yourself.