I did some research about this and decided to use part of Charles Augustin Sainte-Beuve's answer to what a classic is:
A true classic is an author who has enriched the human mind, increased its treasure, and caused it to advance a step; who has discovered some moral and not equivocal truth, or revealed some eternal passion in that heart where all seemed known and discovered; who has expressed his thought, observation, or invention, in no matter what form, only provided it be broad and great, refined and sensible, sane and beautiful in itself; who has spoken to all in his own peculiar style, a style which is found to be also that of the whole world, a style new without neologism, new and old, easily contemporary with all time.
Such a classic may for a moment have been revolutionary; it may at least have seemed so, but it is not; it only lashed and subverted whatever prevented the restoration of the balance of order and beauty.
I found this at about.com
I have found a few incomplete lists and did not find them satisfying enough as I think there were quite some important authors missing, so I am not going to post a link or links to those lists.