I define a great movie as one you would watch again (and probably have). Such being the case, my top five would be:
5. Raiders of the Lost Ark (but none of the sequels)
4. The Good, the Bad and the Ugly (and any of the other spaghetti westerns in that group)
3. Rocky (but none of the sequels)
2. Casablanca
1. The Big Chill