iPod's aren't ever going to win the "Best Battery Life in the Whole World Ever" Award (primarily because it doesn't exist) although there was a move in the right direction with their new range. However, you can boost it's juice to take advantage of the new movies being put on iTunes (if you're in the US where it's actually happened) by purchasing this Volta. It fits onto the bottom of your 'Pod and increasing the battery life up to 16 hours of video or 80 hours of music. There's no sign of the pricing on the website, so keep checking back.
Product page: Sonnet Volta battery