End credit scenes I can actually say were well worth the wait when I sat down in theaters:
POTC3: Will returns to shore, and meets his wife and child.
Thor: Loki survives, eyes the Tesseract.
The thing is, most stingers would work just as well at the regular end of the movie. If you know the end credits scene is coming, you're going to be disappointed if its kind of lame, like IM3's. But if you don't know it's coming, or if it interrupts the credits pretty quickly, it manages to maintain some of that magic from your first few views.
The best hooks are the ones they mean for everyone to see, not just the geeks. For instance:
Back to the Future II: "No, Doc, I'm back from the future!" "...Great Scott!"
POTC2: "So tell me, what's become of my ship? Hahahaha!"
Avengers: (Mid Credits) THANOS!
Batman Begins: Joker Card.