I generally equate Visconti as the real forerunner of neo-realism, considering his Ossessione predates the major "breakthroughs" of Rossellini and De Seca. However it was rather like the French New Wave in that it was more a general trend and an outgrowth of certain new voices than a direct movement. Its inception was largely influenced by the war and the complete lack of resources. I believe Rossellini had once said that he had no concept of neo-realism he just wanted to make movies and that was the only way he could at the time.

White Nights is one of Visconti's most beautiful films, and I enjoyed it more than Bresson's film from the same book Four Nights of a Dreamer, which is even harder to find in this country. Visconti however was far from a peasant, so for me I feel his best work generally deals with his own social class (the landed aristocracy). He does well with the decadence of this class in Sandra, which remains my favorite film of his. Although thanks to the Criterion collection for finally releasing the most complete version of The Leopard available. Warner Bros, who was his distributor of his later films, has put out Death in Venice and the Damned, and I only hope they get on the ball with the rest of them, particularly Conversation Piece and Ludwig. However Visconti's neo-realist films are certainly worth watching, particularly La Terra Trema and Rocco and His Brothers (although mine is dubbed so I think that detracts a little).

Rossellini's initial WWII trilogy (Open City, Paisan, Germany Year Zero) are all essentials as far as film literacy goes, but his films did occasionally utilize professional actors contrary to many myths and legends about the movement (as did Visconti's later work).

De Seca embraced the movement well, and most of that I think is attributable to his scenarist Cesare Zivittani(?), who collaborated with him throughout his early career. I've not yet watched The Children are Watching Us (although it is in one of my piles), which that film also predates Open City. His films have been attacked in modern film circles as being too sentimental and although his Miracle in Milan is almost overflowing with sentimentality, I find it a rather charming fable. 

Like arguing over whether Godard, Truffaut, Chabrol, or Rivette was the initiator of the new wave, neorealism is also a movement without any defined figure head, but with several big high profile names, who all eventually grew out of it and made somewhat unique films in and out of the system.

I rattled on too much, but luckily most of the key films from Visconti and De Seca are available on DVD, Rossellini has gotten much less love, but it is the centenial anniversary of his birth, so I'm hoping that will motivate more.