1) Ray Liotta as Donnie Brasco in the eponymous film.
2) De Niro
3) Johnny Depp as Agent Sands in Once Upon A Time In Mexico
4) Steve Buscemi as Tony Blundetto in The Sopranos
5) Christoper Walken as Vicenzo Coccotti in True Romance
6) Harvey Keitel as Mr White in Reservoir Dogs
7) Harvey Keitel as Vincent "The Wolf" Wolfe in Pulp Fiction
8) Al Capone
9) Steve Van Zandt as Silvio Dante in The Sopranos
10) Dominic Chianise as Junior in The Sopranos
That covers them all I think, not sure on The Sopranos ones because I've never got into watching it and I'm not sure about the film that 2) was from so I've left it out rather than guessing. A lot of the above aren't actually mafia, they might be criminal but that is rather different than being from the Cosa Nostra. Maybe someone else would like to correct me where I've gone wrong.