Try Piers Anthony. Start off with his early Xanth novels to get a bit of a taste of his simpler work, then gradually work your way up to the Incarnations of Immortality, and end off with his Blue Adept series. Maybe even his fairly early Tarot novels in there for a bit of fun.
His stuff has to be done in stages, though, really. Plunging head first into Bearing an Hourglass might strain the mind a bit, depending on what concepts you're used to.
