My fellow senior from hgih school has an idea for the 4th movie:
Jack finds the fountain of youth, spends a long time there, finds his way to North America, and becomes Johnny Depp.
I don't think there can be an effective fourth. All the loose ends that could've continued the series for a while were tied up. I won't tell about the ending for those who haven't seen it yet (but should cuz it's frickin' AWESOME), but there's really nothing left of the series without introducing more stuff, and that'll just make it go downhill cuz it gets dragged out. A change of pace would be nice, true, but they tied up pretty much everything they needed to. What was left isn't enough for a "final" fourth movie as everyone wants. Unless it's a short little TV special that only lasts an hour...
BUT THE MOVIE WAS AWESOME!!!!!!! I seriously cannot wait til the DVDs come out.