I like the iPod idea for extended warranty. It can be purchased any time during your current warranty, so if your battery looks bad or it starts acting up near the end of your current, you can purchase the extended and get it replaced for free
In my case it cost less than the replacement battery.
*But in general an extended warrant is useless, if it doens't break in the first few weeks, it's likely not going to break under any conditions that the warranty will cover anyway.