"Around The World With Superman" - Superman uses his powers to give a little girl back everything she has lost. He has moments that are more super, but rarely one in which he is more of a hero.
There's also the Season 1 episode, "The Birthday Letter", where Superman gives a little girl stricken with polio a flight around Metropolis. The people's reactions and the girl giving Supes a kiss on the cheek solidified this already heartwarming moment.
In "Tomb of Zaharan", Lois and Jimmy are missing and possibly in trouble (again). Perry is taking the investigation a little too slow for Clark. When Perry tries to stop him, Clark snaps, "Now you listen to me, Chief. Lois and Jimmy mean a lot more to me than any anniversary edition!" and races out of the room. Granted, he may have been a bit hard on Perry, but it's still adorable.
And of course in the first episode when Mama Kent reveals she made Superman's costume out of the material she found him in! No wonder he's never worn another.