Agree with lots of the choices so far. For magic items etc, I like Wayne England. My all-time favourite is probably Tony diTerlizzi's work on Planescape.
I go through phases, as I do with music. Also, I don't remember all the names of the artists whose stuff I happen to like. So sorry to all those I should have named here - you know I appreciate you anyway, right?
Current faves (on a purely visual, instinctive or emotional level, as I ain't no artist, nor art critic):
Jennifer Meyer
Sam Wood
Todd Lockwood
'Udon Studio'
[Nearly all the other artists whose works appear in the stunning 'A Game of Thrones' RPG]
Christopher Shy
Jason Rosenstock