I liked the Silmarillion, too, but yeah that's not the first time I've heard someone compare it to the Bible.
I'll second that Terry Pratchet, Neil Gaiman, and Frank Herbert are three of the very best fantasy/scifi writers out there.
I'll also highly recommend Gene Wolfe. Easily, and consistently, one of the best writers (of fantasy, or otherwise) of this century.
John Crowley's 'Little, Big' is one of the best books, ever. The Solitudes isn't bad, either, but I'm having trouble getting through it. That's likely more me, and less Crowley, though.
Azimov is...ok, but I can live without him.
Heinlein's not bad, entertainment-wise, but he had a lot of agendas going on.
Ray Bradbury is excellent. One of my absolute favorites for sci-fi.
Robert Jordan's writing is just awful. Always has been.
Raymond E. Feist: Stick to 'Faerie Tale', 'Magician', 'Silverthorn' (it's not very good, but it's in the middle of two good books), and 'Darkness at Sethanon', as well as the 'Empire' collaboration with Janny Wurtz (who's quite a good writer, herself, by the way--I recommend 'Master of Whitestorm'.). Anything Feist wrote after those gets steadily more awful.
George R R Martin's 'Song of Ice and Fire' started out great (the first two books and the short stories), but the writing quality's really getting ugly.
David Gemmell isn't bad. Maybe not consistently great, but good for passing the time. I'm surprised noone mentioned him.
If you want to try something really interesting and out there, sci-fi wise, I suggest George Alec Effinger, particularly his 'Marid' series.
I also recommend Steven Brust's 'Cowboy Feng's Space Bar and Grill'. I like his Dragaera series, but I wouldn't call them his best work.