There's some kind of weird irony. The Neverending Story should not have a sequel. Frankly, I only saw the first one, and I thought it would er.. never end.
But I would have to say the ultimate 'never... ending... story..." (to get my context right, you would have to beat your head against the table while saying one word to each smack) would have to be the Land Before Time, part 17 or wherever they're at. I imagine they'll be arriving at the Land During Time after a few dozen movies. Or maybe the Great Gazoo will show up and try to throw in a good twist to the tired plot.