There have been some that actually consider Sicilian a whole different language rather than a dialect. It has the influence of so many different cultures, Norman, Arab, Greek, and so on, that it can be very different than what it spoken in Rome, for example.

As carmela has correctly pointed out, however, the more recent generations have been losing that and been mainstreamed. It's sort of sad, IMO.

I think that DeNiro's Sicilian in GF2 was probably as close as we're ever going to hear on the big screen, especially here in the US.