He created Cloak and Dagger? Nice.
David Michelinie. He doesn't get nearly enough praise. He basically set up everything we know about Spider-Man for 3 decades.
This. His run was absolutely great, but everyone seems to give all the credit to his artists.
Also, seconding Bill Mantlo. Really liked his stuff.
I think it would be hard to claim that Peter David is overlooked or unsung, but I think his Friendly Neighborhood Spider-Man series never quite got the credit it deserved. I think between his stories and Mike Wieringo's art, that was a series that had me more interested in Spider-Man than any other book in the 616 has. It had a fun classic feel, while still pushing Peter's narrative forward and creating some really compelling new villains, that I've never seen since.