Eric Eddison, with his Worm Ouroboros would be probably only high fantasy (in modern standards) author to predate Tolkien. However, pulp fiction had a strong heroic fantasy scene, championed by Robert E. Howard. Also many works of Burroughs could be consider as heroic fantasy- Pellucidar, Venus, Caspak or Barsoom series comes to mind. Abraham Merritt was another famous writer working on what we today would call "fantasy".

In short, answer is Pulp- like "Weird tales" and such. Many talented (and even more mediocre and awful) writers were making fantasy stories for whose journals. However before JRRT most- if not all- fantasy was sword and sorcery/heroic fantasy. It was a genre of short and light adventure stories.