Rod Ruth, illustrator of children's books like Album of Dinosaurs and Baleful Beasts and Eerie Creatures -- which I compulsively checked and re-checked out of any number of childhood libraries and public school media centers as a child -- is an unsung master. Everything he painted was filled with mad, vibrant energy and color (and often, terror).
If I could commission RPG artwork from anyone who has passed beyond the veil, this man would be near the top of the list.
(Yes, this post is laughably low on content. It's been an extremely busy week for me.)