What are the existentialist elements in Estragon and Vladimir from Waiting for Godot?

Vladimir and Estragon know exactly what they are waiting for. They are waiting for a man named Godot because they expect him to give them a handout. Godot knows they are there and are waiting for him. He intends to go to meet them, but he is taking his own time about it because these two tramps are so insignificant that he doesn't care how long they have to wait or whether they decide to leave.

During the play a boy arrives on two occasions to tell the waiting men that Godot will not be coming today but will be there tomorrow. It seems overly speculative to conjecture that Godot does not exist or that Godot is God. Samuel Beckett is "holding the mirror up to nature," to use Shakespeare's definition of drama in Hamlet. Beckett is asking his audience, and in fact each one of us, in effect, "What are you waiting for? These two men are tramps, the lowest of the low--but at least they know what they are waiting for. They are waiting for a simple handout from a real man whom they know and who knows them. Do you know what you are waiting for?" Probably many of us would have to admit that we don't know and have never known. Although we might also admit that we have been waiting for something--and are still waiting.

In David Mamet's excellent play Glengarry Glen Ross, he has Shelly Levene, one of his salesman, say the following to a couple of prospects on a "sit":

"This is now. This is that thing that you've been dreaming of, you're going to find that suitcase on the train, the guy comes in the door, the bag that's full of money. This is it."

Beckett's audiences may not understand half of what is going on, but many of them must realize that they are like those two tramps. They are looking in the "mirror" being held up to nature. They are hoping to find that suitcase on the train which is full of hundred-dollar bills--or indulging in other fantasies while life goes on in its daily grind and every day each of us grows one day older. 

But at least Vladimir and Estragon know what they are waiting for. They are waiting for a real, live man whose name is Godot.