E. Hoffman Price would be one I would recommend. A pulp writer who found success in many different genres of pulp, his greatest bit of interest would be that he is the ONLY contemporary of Lovecraft, Smith and Howard to have met all three in person.
Nobody has mentioned Robert E. Howard? Lovecraft had this to say about him "for stark, living fear what other writer is even in the same league". "Pigeons From Hell" is one of the best bits of short horror fiction of that century. For that matter, all three of Howard's piney woods tales, "Black Canaan" and "The Shadow of the Beast", being the other two are excellent examples of regional horror NOT set in New England from the Weird Tales era. "The Black Stone" is one the best horror stories related to the Cthulhu Mythos(if you believe in that sort of thing and do not dismiss it as mere Yog Sothothery on the part of contemporaries attempts to have a bit of fun with their friend's work. I don't subscribe to the whole business of the Cthulhu Mythos) not written by Lovecraft. "The Worms of the Earth" is about as close to Shakespeare as you will find from the period. Enough of my Howard grandstanding.
A neat idea would be to put out a blister containing an author and one of his characters. Lovecraft and Armitage or Randolph Carter, for example. Howard and Kathulos, maybe.
Ryan