X-Men #4 (Marvel, 1964)

The only page from this issue ever to come on the market so far. Kirby only did full pencils (as opposed to breakdowns) for the first ten issues of this title, so there are very few fully-penciled splashes to go around. And having the whole team in the danger room is an ideal motif. A very cool bonus appears on the back of the page: handwritten prototype names (by Kirby we presume) for the Scarlet Witch, who made her first appearance later in the issue (Witch Woman, Jinx, the Sorceress, and quite a few others)!