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.
X-O Manowar from Valiant lasted 70 issues. They actually had two #50s numbered 50-X and 50-O.