Batman #312 is an absolute classic, I had a UK reprint of this when I was a kid. I wish we got more smaller-scale stories like that these days.
Calandar man was also in Shadow of the Bat's "The Misfits" by Alan Grant teaming up with Killer Moth, Catman and Chancer. Here he was portrayed as a dopey loser whose obsession with dates is more a source of humour than an actual threat, however, he does get a good character beat at the end showing deep down he's not an awful person.
There was also a fun 80-page giant (or something) where he tried to blow up Gotham because he missed the turn of the year 2000 (and ripped off Anarky's costume in the process).
Honestly, I really liked the recent Long Halloween special (despite myself). It goes to show that with the right story any villain can be a threat.
There was a really neat Easter Egg in batman: Arkham City where Julian was left in a cell under a courthouse and if you went to him on a specific (holi)day each month he'd have a different line of dialogue. Once you'd seen all twelve, the next day he'd have escaped.
Also, I legit laughed out loud at his cameo in The Suicide Squad. Did not expect to ever see live-action CM!