Who would've thought lines like "You're gonna need a bigger boat." and "Here's lookin' at you, kid." were never actually written into the script?  They are perfect lines for those moments!  There are several others that might surprise you too.

I love a good list and I love it even more if it is in video form. This is the "25 Greatest Unscripted Scenes in Films." It may not be from a formal publication, but it is a good compilation by a person who has done many others.