Certainly NOT Dead Like Me. Still salty about that one.
Serenity and Star Trek as others have said are proabbly my actual favorites. The original Naked Gun movies were based on the short-lived Police Squad show and are as close to maintaining continuity as anything ZAZ could be. Then, the original Transformers animated movie gets more credit than it deserves due to nostalgia and not being a Michael Bay mess, but it had no business being even as good as it was.