If you are at all like me, you are counting the days until May 23, 2014 in anticipation of X-Men: Days of Future Past. As I did previously for X-Men: First Class which you can find here, I put together a 1st appearance list for all of the characters that we know about so far. There is one other that should probably be on this list, but I'll wait until the movie comes out in case anyone is avoiding the spoilers. Also worth noting is that the story is based on Uncanny X-Men #141 and #142.
The (Uncanny) X-Men #1: 1st Appearance of Professor Xavier, Magneto, Beast, Iceman
The (Uncanny) X-Men #4: 1st Appearance of Quicksilver
The (Uncanny) X-Men #14: 1st Appearance of Bolivar Trask
The Incredible Hulk #180: 1st Cameo of Wolverine
The Incredible Hulk #181: 1st Full Appearance of Wolverine
Giant Size X-Men #1: 1st Appearance of Storm, Colossus
Ms. Marvel #16 - 18: 1st Appearance of Mystique. This one is tough to judge. Mystique cameos in #16, disguises herself as Nick Fury in #17, and makes her first full appearance as Mystique in #18.
The (Uncanny) X-Men #129: 1st Appearance of Kitty Pryde
Avengers Annual #10: 1st Appearance of Rogue
Marvel Graphic Novel #4 (The New Mutants): 1st Appearance of Sunspot
Marvel Graphic Novel #5 (God Loves, Man Kills): 1st Appearance of William Stryker
New Mutants #16: 1st Appearance of Warpath
Uncanny X-Men #282: 1st Appearance of Bishop
Uncanny X-Men #317: 1st Appearance of Blink