Moebius’ stuff is interesting and I mostly like it.
Ted Nasmith is quite good, with great detail and character, though I tend not to imagine the composition of Tolkien stuff differently.
I like the much of the art from the first publisher of my first favorite fantasy RPG The Fantasy Trip, so Roger Stine (but specifically his TFT art ), Pat Hidy (example example example ), and Robert Phillips ( example example ).
This is a classic RPG image I like. (“Titan,” aka “Dragonspell,” by Chris Achilleos for the full wraparound cover of Titan: The Fighting Fantasy World, Puffin Books, 1986).
I’m not much of a fan of superhero comic book art.