Issue #16 of Stan Lee's original run, when Hank Pym, Janet van Dyne, and Tony Stark all decide to temporarily leave the team to get some rest from the constant exhaustion of fighting supervillains. When Captain America returns from a trip from South America, Hank immediately picks him up(in his giant form) and starts fooling around with Steve in a playful manner, leading Pietro and Wanda Maximoff, who are the new replacement members(along with Hawkeye), wishing that the X-Men or the Brotherhood of Mutants could have this kind of camaraderie. Also, Hank and Janet and Tony wishing one another farewell(they aren't aware of the other's identities at this point) and speaking fondly of the other as the issue ends. It's a very tender story overall.
The Vision is accepted into the Avengers after fighting against Ultron. He leaves in his usual stoic nature but only to show he is very human and begins crying in joy, shedding a single tear in a wonderful one-page panel.