The Greyhawk Deities were not in the 1e Deities & Demi-Gods. Gary's Greyhawk Deites were, originally, in Dragon Magazine issues 64, 68-71 and later collected in the Box set as I recall.Out of the box suggestion: check out the 3E Deities & Demigods, where the Greyhawk pantheon and cosmology gets detailed pretty heavily. 1E Deities & Demigods might be good for that, too, bit I like James Wyatt's take.
In addition, there were the Roger E Moore Articles on demi-human deities (Dragon Magazine 58-63) and Lenard Lakofka's Suel Pantheon (Dragon Magazine issues 86-90) if one wants to include them.