If you're an iPod fanatic (you know who I'm talking about) you'd better have a sit-down. Xlr8yourmac recently reported that after they replaced their original iPod battery with one from Newertech they went from 4 hours to 21 hours of playtime. It cost them $40 and five minute's effort, (although this definitely voids the warranty). The $40 includes a tool set and installation guide, and if you tack on the coupon code 'HIGHROAD' when you check out you can get the NewerTech RoadTrip FM Transmitter device for only $9.99. Not bad, especially if you've got an older iPod (1st or 2nd gen) with a worn out battery.
Update: Some people are having problems with the RoadTrip code, so don't hold me to that.