Well, I know this isn't Disney (it was going to be a Disney film until the company dismissed the movie), but nevertheless it's still one of the most tearjerking moments. It doesn't help that John Williams composed the background track, which makes everything really sad.
If you want an actual Disney movie, there really isn't any better than Mufasa's death. That could make any grown man bawl like a baby!
Disney, however, doesn't tend to make tearjerking moments because the movies are all centered around "Happily Ever After" endings. It's mostly in their classics that you will find it.
Because of the nature of this topic, I'm going to post a video that will make you happy. :)