My favorite episode is "The Great Brain Robbery," in which Dr. Fate inadvertently causes The Flash's mind to be switched with Lex Luthor's. This gave Michael Rosenbaum a chance to play Luthor as adult in Flash's body, and let Clancy Brown do his impression of Rosenbaum's Wally West.
Just when I was lamenting JLU's passing, I saw word of the direct-to-DVD Justice League: The New Frontier. The following is from Wikipedia:
Justice League: The New Frontier adapts Cooke's award-winning mini-series DC: The New Frontier. Set in the 1950s, the story bridges the gap between the Golden and Silver Ages of comics in the DC Universe. The film will focus heavily on two main stars, Hal Jordan (Green Lantern) and the Martian Manhunter. However, dozens of DC characters could potentially appear, echoing the book's huge cast. "We are going to honor as many characters as possible," Noveck confirms. "The decision has been made, however, that where the story calls for it, we are not going to have just a random 'Joe Blow.' It will be somebody." Also central to the story will be Barry Allen, a.k.a. The Flash.
Superman, Wonder Woman, and Batman -all of whom played major parts in the mini-series- are expected to play a part in the film.
So far the only characters confirmed are Superman, Batman, Wonder Woman, Martian Manhunter, Green Lantern, Flash, Aquaman, and Robin. It was revealed in an interview with Phil Morris (who is playing King Faraday in the film) that Neil Patrick Harris will be playing Flash. Ain't It Cool News reported that David Boreanaz will voice Hal Jordan, and Brooke Shields will voice Carol Ferris.
IMDb lists Kyle MacLachlan voicing Clark Kent/Superman