Here are a couple of interesting texts concerning the rapture of the Church occuring before the Tribulation.
“Behold, the days shall come, that they which dwell upon earth shall be taken in a great number, and the way of truth shall be hidden, and the land shall be barren of faith.” Ezra, ~400 B.C.
“For all the saints and the elect of God are gathered prior to the Tribulation that is to come, and are taken to the Lord lest they see the confusion that is to overwhelm the world because of our sin.” – Ephraim the Syrian 373 A.D.
These two texts prove the theory of the Pre-Tribulation Rapture was understood and taught from ancient times.
The Biblical evidence and reasons I believe in a Pre-Trib rapture can be found here.