I remember the Nostalgia Critic's "Top 11 Simpson's episodes" actually making a good case for the moral of "Bart Gets an F". Really, we're practically inundated with the message that "if you put your mind to it, you can do anything", extolling our supposedly limitless potential and the value of hard work. Both are worthy morals in and of themselves, don't get me wrong, but I agree with Walker that the converse, that "sometimes even with hard work you will fail" is also something we need to see from time to time.
Also, the ending to Mrs. Doubtfire. Stories centered on divorced characters have a strong tendency to have the divorcees get back together (or are put on the fast track to it) for some reason or another. Mrs. Doubtfire, by contrast, actually heavily implies that Robin Williams and Sally Field's characters do indeed have irreconcilable differences (their penultimate scene together quickly devolves into them yelling at one another again before they catch themselves), and while they do come to an understanding there's very little in the way of implication that they'll ever get back together, and a small monologue at the end punctuating the point and elaborating on it quite beautifully.
Also, the ending to Mrs. Doubtfire. Stories centered on divorced characters have a strong tendency to have the divorcees get back together (or are put on the fast track to it) for some reason or another. Mrs. Doubtfire, by contrast, actually heavily implies that Robin Williams and Sally Field's characters do indeed have irreconcilable differences (their penultimate scene together quickly devolves into them yelling at one another again before they catch themselves), and while they do come to an understanding there's very little in the way of implication that they'll ever get back together, and a small monologue at the end punctuating the point and elaborating on it quite beautifully.