My personal favourites are:
'Dune' by Frank Herbert, vastly superior to the new books by Brian Herbert and Anderson (Battle of Corrin being just another disappointment). Still my favourite science-fiction book all times.
'Ilium' by Dan Simmons, almost as good as 'Dune'. Second part 'Olympos' being released this month and I just cannot wait!
(Hyperion being good too ofcourse, just that this 'Ilium' is even better)
'The Deathgate cycle' and the Dragonlance books by Weis&Hickman, I did not care for 'Rose of the Prophet' and definitely not for 'The Darksword' series. 'The Sovereign stone' however is pretty good but seems to suffer from a problem that Weis&Hickman have: they can create a perfect setting and story, but they seem to lack the ability of creating a good ending to that story. (even The Deathgate cycle has an ending that just feels like they couldn't find anything better, IMO)
'The chronicles of Cadwal' and 'Lyonesse' are two very good reasons for reading Jack Vance, for some reason Vance is just rarely mentioned in lists and that I find a pity. These two trilogies are excellent reading, with Vance's special style (especially his characters can be a bit weird at times) but very enjoyable.
'The world of Tiers' by Philip José Farmer. Another classic, IMO again ofcourse, but the final two parts of the series are not good at all, it is mainly the first three parts that are very good. (which leaves two parts that I found agreeable, not great but not that bad either)
'The many-coloured land' and the prequels to it by Julian May.
As for other writers, too many to name really, especially when I start to think of fantasy and science-fiction. Asimov, Heinlein, Philip K.D.ck (lol, can't write his name), Pratchett, Haldeman,...