Definitely, for me, the world of Malaz (Steven Erikson and Ian Esselmont series of books) is the most impressive, coherent, vibrant and exciting fantasy world ever described. I'm a big fan of Tolkien, but I rate The book of the Fallen even higher. The first step (Gardens of the Moon) may seem difficult, but the reward woth the effort once you've fallen in.
Otherwise, The 7 kingdoms (Iron Throne) is a must and of course Dune. Purists will say it's not "fantasy" but it's an incredible imaginary world.