Justice League of America #21 (1963)

In this early adventure of the Justice League of America, readers are treated to a true gathering of champions with the first ever team-up between the JLA and the Justice Society of America.  When villians from both Earth-1, the mainstream Earth of DC continuity, and Earth-2, the alternate reality where the Golden Age heroes of the DC universe remained for years, combine forces and commit crimes across both universes, it is only the combined power of the premiere super teams of two universes that is capable of preserving justice and order.  This classic cover depicts the Justice League trapped in their headquarters and calling out across the dimensions to the Justice Society for assistance.  Penciler Mike Sekowsky, inker Murphy Anderson, and letterer Ira Schnapp bring together this seance-inspired, historic teaming of legends.  Notice especially the Martian Manhunter of the 1960s, which more resembles Lex Luthor with a digestive disorder than the Martian that fans of the Modern Era know so well.  

Alpha Flight #2 (1983)

Created as part of Wolverine's origin story in 1979's X-Men #120, John Byrne's Alpha Flight, one of comicdom's few Canadian super teams, received its own series in 1983.  The majority of the team's roster had distinctly Canadian traits or backstories, such as the Inuit influences behind the characters of Shaman and Snowbird.  The series had a fairly successful run for eleven years and has been the subject of more than one revival attempt, the most recent in 2007.  Byrne himself stayed with the series for the first twenty-eight issues serving as creator, writer, and artist during that tenure.  As part of that body of work, we have the cover of issue #2, showcasing the artist's deft handling of expression and multiple characters.  Note especially the contrast between the optimistic concern of the hirsute Puck and the brooding malignance of his troubled comrade, Marrina.

Tales to Astonish #13 (1960)

One among many of the iconic covers of Jack Kirby, Tales to Astonish #13 gives us Groot, the Monster from Planet X.  Memorable more for humor than horror, this classic image was birthed during the Mighty Marvel monster craze of the 1950s and 1960s.  Like only he could, Kirby conveyed an imposing menace with crisp lines and a forced perspective of a once proud metropolis crushed under the weight of Groot's massive, branching root system.  In an admittedly silly story, it is the timeless art of Jack Kirby that conveys all the mustered menace of an alien composed of wood.