To expand on what
@wagglyplacebo said, despite its name, the Black List is actually a list of the best unproduced screenplays in Hollywood. A lot of films from the list can go on to be produced, or if not it's a very good start to a screenwriter's career.
Passengers, which is coming out later this year was a Black List script and so was
The Imitation Game a couple of years ago.
That said, "best" is a very subjective term and I've read some terrible Black List scripts.
American Hustle started life as a Black List script called
American Bullshit, which is
even worse than the film they ended up making (which felt like a first draft anyway). Also, I've read
Untitled Lax Mandis Project and it's objectively awful, but it gets full marks for pissing this guy off. I could post the script here if anyone's interested.