Nice job - this was the first Critter Cache I've gotten, I'm glad to see the Goodman team-up with Chaosium allowing products like this one. There are definitely enough left-over Cthulhoid Mythos monsters for a second critter cache... Cthonians, various Great Old Ones and Outer Gods (Shub, Hastur, Yog-Sothoth, Azathoth), Insects of Shaggai, Hunting Horrors, the Son of Yog Sothoth, Dimensional Shamblers... you get the idea.
Any chance we'd see a general 4E sourcebook for CofC style adventures? Magic in Call of Cthulhu is mostly ritual-based and could convert to 4E fairly well - the 3.x era D20 CofC book had a section on sanity loss for fantasy characters, sanity values for standard monsters, how to mix fantasy and CofC, etc. Could be a hit for you guys!
Lessee, Mythos Rituals, artifacts, books and grimoires, monsters, some delve-style encounters, (potentially) a sanity-sub-system, and notes on developing a mythos-oriented campaign in 4E would be a fantastic sourcebook.
Just to clarify, this book is not the result of a team-up between Goodman Games and Chaosium. All of the Lovecraftian monsters that appear in this book are taken from the works of H.P Lovecraft that are now in the public domain. Monsters such as cthonains, the insects from Shaggai, and the dark young of Shub-Niggurath, to name a few, are the creations of other authors and are not in the public domain. Chaosium, I believe, holds the rights to most of the Cthulhu Mythos stuff that is not directly from Lovecraft's own works, so that's why none of that material appears in Critter Cache: Lovecraftian Bestiary
I think a book on Lovecraftian magic is a great idea. However, as I mentioned above, it would have to come from Lovecraft's own works rather than material owned by Chaosium.