It's true that Anniversary issues were great in those years!

Conan the barbarian #100 was such a huge milestone that the book arguably never recovered from it! It was the final chapter in the story of The Queen of the Black Coast, which had been going on for several years. Real epic issue.

Legion of super-heroes #300 is another I really enjoyed. It resolved a cliffhanger set up in previous issues and showed how the "Adult Legion" stories from the past fit in the book's continuity (or not).

Combining several good stories, several resolutions and having an impact over the series as a whole, it was all an anniversary issue should be. (Guest spots by several famous artists who had worked on the mag, too).

That's pretty impressive. I was more of a Tintin reader when I was young, but Spirou was a fine mag... I wish those periodicals had all managed to thrive (Tintin, Spirou, Pilote, Métal Hurlant, À suivre...) I wonder how Spirou pulled it.

I was myself more of a Pif/Rahan kid, but Spirou's success is all age, diversity, and affordable, always has been. Metal Hurlant's always been boy only, Tintin too, Pilote could have pulled it but started to favor their older audience. A suivre, I thought was still around, hahaha

I had forgotten about Pif!!! I was very surprised to learn, years after having been a regular reader, that it was published under the aegis of the Communist Party! (No wonder Rahan was such a do-gooder of a caveman!) 

There was also a Lucky Luke magazine for a while (that's where Alexis McCoy was first published, I believe) and a six-issue run of Achille Talon magazine. I treasure the latter because it's rare, even if in all honesty it wasn't that great.

Right now, I'll have to vote for JLA #200, but the Legion of Super-Heroes #300 is right up there. As others have mentioned, Avengers #100 and Uncanny X-men #100 were great ones, too. I did think Brave and the Bold #200 and Uncanny X-Men #150 were also very good.

Also, Avengers #200 has just about the best cover of any anniversary issue, with the possible exception of JLA #200, but the interior contents don't quite match it, so say the least.

I'll nominate Fantastic Four #100 as one that should be given consideration. Perhaps not the most interesting story - the FF just spend the entire issue in a running battle against the Puppet Master's facsimiles of nearly every enemy they've ever faced (and they all seem to be nearly as dangerous as the originals, which should make the Puppet Master one of the most powerful villains in the MU, shouldn't it?).

But the Kirby/Sinnott artwork elevates to another level and also my favourite FF member, Crystal, gets to save the day (again!) in what must have been one of the last stories she was drawn and co-written by Kirby, and thus one I would advise all writers to pay attention to when writing the character. Also there's a lot of nostalgia working because it's one of the comics I owned as a younger kid - didn't have too many at that age (I would have been around 8 years old when it came out).