Early Blanche till the end of 3rd ed, there was a visions in those and it was going in lots of ways, his take on the 40k universe with confrontation is also splendid. Though I love the graphism of his work after that, I think it became a bit more "monotone" with always the same colours, subjects and Grim Darkness (making everything religious in some way)
Jes Goodwin, though his sculpting his top-notch, his drawing is on par too, his space hulk/40k drawings are so evocative
Adrian Smith, first he's got the same name as the Iron maiden guitarist and that has to count for something and 2nd : He was the best drawer of both RoC tomes. His ability to capture teh essence of any race or setting he draws for is just mind blowing. Hi schaos is perfect, his orks are brilliant, his tyrannids are unrivaled and his eldar have the perfect fragile/deadly ratio...
I know it's not all about fantasy but hey, what's the difference?
If I remember right, we had a poll on this very subject some time ago no?