I am SO damned surprised nobody has said "Clifford" yet. That movie sucked so bad, it's literally the only one I didn't give more than 20 minutes for a chance to save my rental fee before I ripped the blasted thing out of my VCR...and I've rented hundreds of movies.
Many of the other movies posted here were much better...some I even like and have seen more than once. Rent Clifford, see if you don't change your vote...