Back again, with more.
These are artists whose work you've seen, even if you don't recognise the names:
Brian Froud. Froud not only paints fairies (oops, I mean 'faeries') but apparently visits and chats with them, too! Has worked with Patricia McKillip, Charles Vess and Terri Windling. Author/illustrator of the ubiquitous 'Faeries', and the 'Lady Cottington' books.
His wife, an artist in her own right, is the designer/creator of Yoda, as well as characters from 'Labyrinth' and 'The Dark Crystal'.
John Howe - arguably the best illustrator of Tolkien's works. That picture of Gandalf, on a wind-swept hillside? Yep, that's his. He was also one of the concept artists for Peter Jackson's LOTR trilogy.
Has also done illustrations and covers for Robin Hobb, Guy Kavriel Kay, Roger Zelazny and David Gemmel amongst others, as well as publishing a number of portfolios of his fine art.
Michael Whelon - if you didn't know his work, you probably wouldn't be here. Most acclaimed cover-artist of today. Heck, he did the cover for the American edition of 'Runes'. And he's illustrated for dozens of eminent sf/fantasy authors, from Isaac Asimov to Stephen King. Plus he's published numerous collections of his non-commissioned works, which he describes as 'visionary art'.