Lord Dunsany was to the first half of the 20th century what J.R.R. Tolkien was to the second half. He set the standard for what fantasy fiction was and should be. H.P. Lovecraft got his start writing Dunsany knock-offs and all the early fantasy writers admired him. As late as the 1980s Larry Niven was doing Dunsany-like fantasy shorts.

I have to agree with Dan about Lin Carter's deserving credit for championing him. I first discovered him in L. Sprague de Camp's fantasy anthologies which preceded the Ballantine books by nearly a decade, so let's give him a cheer too.

The latest Dunsany anthology I know of is In the Land of Time: And Other Fantasy Tales which contains stories from his entire career, not just his fantasy stories. Dover also has a book called Wonder Tales which is an omnibus of The Book of Wonder and Tales of Wonder, Dunsany's first two books. The stories are all fairly short and beautifully written, though they have a deliberately archaic style.

Very worth looking into.