Key episodes from Batman: Gotham Knights or whatever you call the WB Batman series:
"Holiday Knights" - Introduces Batman's new costume and the Joker's new look.
"The Demon Within" - Introduces Etrigan/Jason Blood and Klarion the Witch Boy. All right, the latter hasn't appeared in JL(U) yet, but it's only a matter of time, right?
"Girls' Night Out" - Harley, Ivy, and Live Wire vs. Batgirl and Supergirl. It's team-up episodes like this (okay, team-up episodes better than this) that made JL possible.
"Beware the Creeper" - The Creeper, who keeps popping up in minor roles in JLU episodes, debuts.
"Mad Love" - Okay, Harley's not a vital character to JLU, but it's a good episode besides.
Key episodes from Superman:
"The Last Son of Krypton Parts 1-3" - Duh. Not only is this the origin movie of Superman, one of the Big Seven (or the Big One), but it's also our first look at Brainiac, Lex Luthor, Lois Lane, and Jor-El, all of whom make appearances in JL(U).
"Fun and Games" - Gives us the Toyman, Superman Revenge Squad member.
"The Way of All Flesh" - Introduces Metallo. See above.
"Feeding Time" - Rudy Jones becomes the Parasite, who seems far more dangerous in JLU's "Clash."
"Stolen Memories" - Introduces Brainiac, main baddie in "Twilight" and Static Shock's "A League of Their Own."
"Speed Demons" - The Flash becomes the third of the Big Seven to make his debut in the animated universe, and the Weather Wizard is introduced. He naturally goes on to menace the League in "Hereafter."
"Tools of the Trade" - Darkseid's first appearance.
"The Main Man Parts 1&2" - Related to JLU in a roundabout way, in that the intergalactic zoo is a part of the Fortress of Solitude (seen in "For the Man Who Has Everything") and leads to the plot in "The Call" in Batman Beyond, our first introduction to the JL(U).
"Ghost in the Machine" - The first appearance of the Brainiac/Luthor team.
"Apokolips, Now! Parts 1&2" - Our first real introduction into Darkseid and the world of Apokolips. Naturally, many of the New Gods appear.
"World's Finest Parts 1-3" - Batman and Superman team up against Lex Luthor and Brainiac. If anything directly led to Justice League's existence, it's this.
"The Hand of Fate" - Our paltry introduction to Leaguer Dr. Fate.
"Prototype" - JLU member Steel first appears.
"Little Girl Lost Parts 1&2" - Supergirl debuts.
"Knight Time" - Superman and Robin save Batman from Brainiac. Sentences like those are why I love these shows.
"In Brightest Day" - We meet our first Green Lantern (Kyle Rayner, boo-yah!) and Sinestro.
"A Fish Story" - Introduces the League's most useful and versatile member, Aquaman.
"The Demon Reborn" - Batman and Superman against Ra's al Ghul.
"Legacy Parts 1&2" - Arguably the best story of the entire series, fittingly the last. Superman kidnapped and brainwashed by Granny Goodness to believe that he is Darkseid's son. He leads the Apokoliptian invasion of Earth, fights the government, and eventually confronts Darkseid over the deception. Plotlines from this episode, from Superman's betrayal of Earth to Supergirl's injuries to Darkseid's violations, are referenced and followed in JL(U), very subtly in "Secret Origins" and more importantly in "Twilight" and the whole of the first two JLU seasons. Did I mention the episodes were fantastic?
Next time: Batman Beyond and Static Shock!