The Incredibles. Phenomenal script, great action (the visuals have aged fairly well imo), well-realized, entertaining characters, and a pretty unique theme/message. Of course, it isn't the only film with all these kinds of things going for it, but it all comes down to personal enjoyment, and I've found that The Incredibles just never grows stale for me. I've seen it so many times, but if anything it seems to improve with each viewing. American Beauty and The Dark Knight are other candidates, but they don't have quite the same invulnerability to repetition.