Riddler

The Golden Age

Detective Comics #140 - The Riddler! (1948) - The first appearance of the Riddler, can be found in Batman: Arkham - The Riddler.

The Silver Age

Batman #179 - Clay Pigeon for a Killer (1966)- An in depth look at the Riddler's character and obsession with riddles. Fleshes out the Riddler despite most villains at the time being two-dimensional.

The Modern Age

Inspired by Batman the Animated Serie

The Last R?ddler Story (1993) - The Batman Adventures #10 - Edward Nygma is released from Gotham State Penitentiary and he has a scheme that might beat batman. Guest staring Mastermind, Mr. Nice and the Perfesser. (collected in)

A Christmas Riddle (1996) - The Batman and Robin Adventures #3 - The Riddler invades a holiday gathering of Gotham's most famous fathers and sons in order to expose Batman and Robin, whom he deduces must be present. Everyone is suspect and if the Riddler can't figure out which pair is our heroes, he'll simply destroy them all. (collected in)

Notes (2000) - Batman: Gotham Adventures #28 - A popular musician is kidnapped by the Riddler, who proceeds to leave baffling riddles for Batman, Robin and Nightwing. But the joke's on E. Nigma when the musician begins leaving his own clues for our heroes in an attempt to outwit the Riddler! Will the Riddler become aware of these double-crosses and end the musician's career once and for all, or will the Bat-family get hip and make all the right moves to save the chart-topper? (uncollected)

Identity Theft / The Real Deal (2003)- Batman: Gotham Adventures #56-57 - A riddle is left for the Batman, but it seems wrong somehow. Who's stealing the Riddler's shtick? And who's going to get to the copycat first: Batman or the Riddler? - Riddle me this! Bent on proving he’s the smartest of all villains, the Riddler goes one-on-one with Robin, preying on the teenager’s worst fears. (uncollected)

Poker Face (2004) - Batman Adventures #11 - Riddler's reformed, but he still can't stop planting riddles, forcing Batman to put him to good use ! And in the backup, can Riddler keep himself from turning a bank errand into a bank robbery ? (collected in & collected in)

90s

Dark Knight, Dark City (1990)- A storyline combining Batman and the Riddler with the supernatural.

Batman: Run, Riddler, Run (1992) - Riddler is forced to team up with Batman after they are both targeted by government-endorsed security forces.

Detective Comics Annual #8 - Questions Multiply the Mystery (1995) - The definitive Riddler origin story. This issue recounts his origin and has the first appearance of his two henchwomen, Query and Echo.

Batman: Riddler and the Riddle Factory (1995) - Offers a unique look at the Riddler where he operates an underground game show exposing celebrities secrets.

Detective Comics #707: Riddled (1997) - A story in which the Riddler teams up with Cluemaster.

2000s

Batman: Hush (2002/2003) - Riddler plays a pivotal role in this storyline which introduced another major player into batman's rogues gallery, Hush.

Catwoman: When in Rome (2004) - Riddler joins Catwoman on a doomed trip to Rome.

Riddle Me That (2005) - A brutal kidnapping involving Riddles causes Riddler to become a prime-suspect.

Detective Comics #822 - E. Nigma, Consulting Detective (2006) - After the Hush storyline, Riddler reforms (After waking from a coma) and becomes a private detective. In the first issue featuring the reformed Nigma, he and Batman go head to head.

2010s

Batman: King Tut's Tomb (2010) - Riddler and Batman team up to take on the new King Tut who has been leaving riddles at the scene of his crimes.

Gotham City Sirens (2010) - An excellently written series, you can't help but feel sorry for Riddler as he is swept along in the Sirens' activities.

Joker's Asylum II: The Riddler (2010) - Joker recounts a tale of when Riddler fell in love with a woman who simply wouldn't love him back.

New 52

Batman #23.2 - Solitaire (2013) - Part of the Forever Evil Villains Month one shots, this is a pretty simple story about Riddler getting some long-desired revenge.

Zero Year (2014) - The new 52 interpretation of the Riddler is an interesting take on him as it has him pull off his largest scheme to date.

DC Rebirth

The War of Jokes & Riddles (2017) - The first major appearance of the Riddler in DC Rebirth, this series pits the Riddler against the Joker. It also characterises Riddler completely different to the norm as he is portrayed as a Hannibal Lecter-esque serial killer.

Many of these stories are collected in Batman: Arkham - The Riddler