Instant HandBrake got an O'Reilly app-of-the-year vote. Rip DVD to iPod. I'll try it with one of the kids on our next plane trip.
Update 12/29/06: I've done one movie in preparation for our flight and another one is pending. It's not fancy -- the "save other" option didn't do much on my machine. I left the defaults alone and it worked. The compression takes a very long time on a G5 iMac -- probably 3 times as long as the movie. It's a task that has to run overnight for a longer movie or a series of tv shows. The results look quite decent.