The DVD Kraftwerk and the Electronic Revolution (2008) got mixed reviews on Netflix where I rented it, but I thought it was fantastic. Clocking in at three hours, it was a little long, but fascinating. It has interviews with music critics and art historians and covers intersting bands from Tangerine Dream to David Bowie's Berlin period. It really covers the early German scene quite clearly from which Kraftwerk sprang. I'll have to watch it again and take some notes.
Also of note: Kraftwerk's website
