1) The Sicilian
2) The Family
3) The Fortunate Pilgrim
4) Omerta

I haven't read The Godfather and The Last Don novel yet. See, the thing with me is that it's hard for me to read the book after i've already seen the movie because i already know what's going to happen. Other than that, i plan on reading The GF and The Last Don novels anyway because those two ranked in almost all your lists.