Annotation: The above references involve only half the works of Casper's article, here is some summary bits from those books used above.
Goodmonth by Gironi Boccanegra in 453CY: A collection of 100 short stories, told in a framing story of ten members of the idle rich from Eastfair who leave town for a month while a plague is going on. Each story deals with love and are quite bawdy, witty and entertaining.
Historical Reign of Ulek by Geohegan Munt circa 50CY: This book romanticizes one of the most popular stories from Ulek history. It tells of the rule of Count Cartair and his knights against orcs and Keolanders.
Reflections of Our Mother by Rolutir, Ovate of Beory in 538CY: Covers the teachings of Beory in regards to farming, human behavior and philosophy.
Doctrinal Commentary by Dantus Allegrini circa 410CY: A winding tale of Dantus in the outer planes in search of his wife. It is a veiled allegory of politics in the Great Kingdom.
The Book of Hours by anonymous priest of Delleb circa 300CY: An exhaustive chronicling of historical events in the Flanaess. Divinations were likely used to find the exact hour of the day these events happen.
The Courwood Travelers by Geohegan Chausard in 459CY: A collection of 23 short stories, in a framing story of travelers from the County of Ulek going to Celene to drink from a magic spring. They are stopped at a pass in the Lortmils by a village elder who makes them each tell a story before they can go on.
The Fables of Dimbles and Dinges by Ibn Al-Muqaffa of Ekbir in 349CY: A collection of ancient 22 fables probably of Baklunish origin, which are now commonly known even in Greyhawk. Each fable ends with a helpful moral.
Levain's Romance by Gerval Bussey in 410CY: A popular poem of social satire. Levain is a peasant who is mistaken for a mighty wizard, and is sought after by a few bickering factions from a nation under attack.
The Wye Canon by Jenkin Wye in 507CY: The first known collection of religious texts written in the common tongue. Wye was a bishop of Rao in Jurnre who wanted to organize a pantheon of good religions into one (Pelor, Rao, Ulaa, Zilchus, Heironeous, Pholtus and St. Cuthbert).
Crosse Ways of Ulek by Andreas Wythe in 155CY: A four volume set detailing the geography and history of the County of Ulek.
Siman and Elimar by anonymous circa 240CY: A morality play about twin brothers parted when their parents die and raised in different families but later crossing paths again on opposites sides of the law.
(Note 1/11/2011: Found this strip was left out of the Greylore series, and have inserted it out of chronological order just so you know.)