Tolkien's going to be near the top of this list: his stories were essentially a side effect of his world building, itself a side effect of his language building.

Eddings' Belgariad (etc) had a brilliant world, the story came naturally out of the world, rather than merely being situated in it.

Herbert, Frank: none of his stories do any world building. You're just supposed to get a glimpse of it from the stories.

J.R.R. Tolkien by a furlong

Adrian Tchaikovsky does a fantastic job of world building.

He has several different series going, and each one is unique.

The Tyrant Philosophers books are completely different than the Children of Time.

Xanth. I mean the puns alone. Seriously though. Tolkein wrote languages and the mythology of his world without real intent for readers to read it. Just to flesh out how people thought and how the world worked.

I think Malazan is pretty spectacular

Robert Jordan wheel of time?

I agree with so many of the comments, but I gotta include Sanderson, especially the world Roshar in his Stormlight books. Multiple cultures spanning 10,000 years with cool plants, animals, weather, and magic that are all connected. Say what you want about his writing or books 4/5 (I don't have issue with either but lots of people do), I think the worldbuilding is top-notch.