Via Wikipedia and eBay I've come up with this list of superbeings created in the 80s or 90s whose solo titles reached issue 50:
Hellblazer (John Constantine)*
Neil Gaiman's Sandman*
* Denotes superbeings who arguably aren't "superheroes" which is why I used the term "superbeing" in the first place.
I came up with 11. Can you add to my list?
Marvel had 4, DC had 4, and Image had 3.
Off the top of my head, Witchblade also made it 100 at least. Hellboy, if you count the sequential sub-numbering of all the miniseries he was at least over 60 last time I was reading 'em and that was at least 5 years ago.
Do you count new characters taking on an old mantle? Conner Kent/Kon-El Suberboy made it to 100. I think Tim Drake/Robin did too. Linda Danvers/Supergirl made it 75 I think.
For that matter Transformers made it to 80 and G.I. Joe something like 140 at Marvel.