Was going through the AH wiki and noticed that there's no Wilbur Whateley in any form (monster, herald, ally, etc.) in any set. Also no Shining Trapezohedron (apart from a mention in a Yuggoth encounter). What else have you noticed?

A complete lack of xenophobia.

Monsters: Sand Dwellers

Ancient Ones: Cyaegha, Zoth-Ommog, too many others

Tomes: Al-azif, R'lyeh Text, Cthaat Aquadingen, many others

Allies: HPL

Xenu's Paradox said:

Wilbur is described in some Dunwich encounters.

I haven't noticed and I can't think of any glaring omissions. The Necronomicon (Al-Azif) is there.

I believe some of the Ancient Ones listed above have been built as custom content available in the Fan Creations section.

Monsters: Shantaks and Sand Dwellers (Summon Shantak does not count)

Tome: The Golden Bough By James George Fraser (Common Item)

Allies: Not in the slightest bit Lovecraftian, but if you fancy going all Wold-Newton: Bertram Wooster, Reginald Jeeves, Bulldog Drummond, Lord Greystoke, Richard Hannay, William Brown, Tintin, Hercule Poirot and Jay Gatsby would all have been around in the 1920's.

On more of a horror theme, go a little earlier and you can run into Cyril Grey and Roderick Burgess.

Spells: Keenness of Two Alike

Jake yet again said:

Do we get a card for each of the twelve volumes?

arkhamresident said:

Only if we get six more copies of the seven cryptical books of Hsan.