Lybrary.com has a great selection of .pdf. Like Redi said, they have Tarbell, Annemann, Hugard, Bobo, Fitzke, Scarne, Giobbi and lots more.
Another great .pdf is Card Magic USA. It has a ton a great material in it from Lee Asher, John Bannon, Marc DeSouza, Nate Kranzo, Max Maven Michael...