The X-Men #29

From February 1967, this Marvel gem pits the X-Men against a genuinely formidable threat announced right on the cover: "The Super-Adaptoid Strikes!" The green, scaly Super-Adaptoid dominates the main image, blasting out powerful energy beams while Angel — wings spread wide — grapples with him in mid-air above a cityscape, with the full roster of Cyclops, Marvel Girl, Iceman, and Beast peering out from the left-hand panels with unmistakable urgency. Writer Roy Thomas and cover artists Werner Roth and John Tartaglione bring a kinetic energy to this clash that makes "When Titans Clash!" feel every bit as dramatic as the title promises.