If you're a fan, there are a lot of great stories and revelations here:
http://www.gq.com/entertainment/movies-and-tv/201010/goodfellas-making-of-behind-the-scenes-interview-scorsese-deniro?printable=trueLike, the famous "you're a funny guy" scene wasn't in the script. It was based on an experience Pesci had with a real mobster. The reactions of the wiseguys in the restaurant (some of them
real wiseguys, BTW) -- the sudden quiet, the uh-oh smirks -- were genuine because Scorsese hadn't clued anybody in.
And an epic casting travesty was averted. Tom Cruise and Madonna were in the running for Ray Liotta and Lorraine Bracco's parts.