The evidence for pre-existence is the Bible passages about the blind man...blind from birth.. if not immediately apparent, seems pretty darn plausible upon further contemplation. The following excerpt from a LDS writing, explains it very well. Excerpt follows....
Perhaps the most salient to consider at this point is the exchange between Jesus and his disciples recorded in John 9:1–2:
"And as Jesus passed by, he saw a man which was blind from his birth.
"And his disciples asked him, saying Master, who did sin, this man, or his parents, that he was born blind?"
Was this a rhetorical question on the part of the disciples? No, the question indicated that the disciples thought one possible answer to the blindness of the man was that he had sinned. Since he was born blind—a fact the record indicates that both Jesus and His disciples knew—then the wording of the question indicates that the sinning must have taken place before the birth of the man, by the man himself. How could the man have sinned, resulting in a punishment of being blind at birth, unless he had lived before he was born?
If the concept of a premortal life was in error, then the Master Teacher had a perfect opportunity to correct His students. His answer is recorded in John 9:3:
"Jesus answered, Neither hath this man sinned, nor his parents: but that the works of God should be made manifest in him."
Jesus then proceeded to heal the man, foregoing any opportunity to correct the concept of the man having lived before birth. Instead, He acknowledged the concept by saying that the man had not sinned. In the words of one non-LDS scholar:
"The question posed by the disciples explicitly presupposed prenatal existence. It will be also noted that Christ says nothing to dispel or correct the presupposition. Here is incontrovertible support for a doctrine of human preexistence.
"It is perfectly reasonable to surmise on the basis of this episode that Jesus and his followers accepted preexistence and thought so little of it that the question of prenatal sin did not even call for an answer."
And that does, indeed make a pretty good case for pre-existence...