Batman: The Animated Series Spotlight: Joker's Favor

Batman: The Animated Series is the best thing ever--it captures the essence of timeless comic book Batman with a touch of organic light hearted humor. Most of all, it features Kevin Conroy as Batman and Mark Hamill as The Joker. Batman Beyond has a very similar feel even with a completely different canvas, and both are part of the Timmiverse (referring to animated productions by Bruce Timm).

One of the best Joker episodes and best overall episodes of BTAS is "Joker's Favor". It follows an ordinary man, Charlie, who has an unfortunate run in with The Joker on a bad day and is held accountable for a favor "sometime in the future". The Joker keeps close tabs and threatens Charlie's family to make sure he keeps his promise. I'll let you watch the episode yourself, or read about it on the web, but here is why it is one of the best:

•  The Joker is actually scary in this episode. He comes across as more of a clown in most of the episodes (which is not really a bad thing--Mark Hamill's Joker brings lightheartedness in contrast to the more somber villains), but I think the realism of the storyline and the fact that he seems to be drawn slightly differently here make it all the more visceral.
• This is Harley Quinn's first appearance ever in the world of the Dark Knight. You wouldn't think so because she's already a comfortable household character. And she makes a grand first impression.
• Spoiler alert! Batman actually laughs in this episode. It's the context that makes it satisfying.

This is one of the episodes I go back to regularly, and I highly recommend it.