I have always had a big soft spot for Roger Dean’s paintings. When I saw Avatar I felt that bits of it were familiar but couldn’t really put my finger on why. Then I was in a bookshop and picked up his book and bam! there was pandora, complete with floating mountains, rock arches and brightly coloured dragons.
I was sure he must have had a hand in the artistic direction of Avatar so I checked it out. It seems not, and there is a lot of conjecture about law suits! Make up your own mind. His site is a little sparse but Google image search will get you a lot.