Actually, social insects such as ants, bees, wasps, and termites would be better subjects for a sourcebook, as they are already organized in a manner superficially similar to an intelligent race's civilization.
The fact that somebody's putting out a book on the ooze-type monsters isn't surprising, given the vast interest they generate. I've always thought they were the most "absorbing" monsters of all (hahahahaha!).
Since DRAGON Magazine recently put out an article which comes close to being X-rated (if you read the mag regularly, you'll know which one I mean), dare I suggest an "Adults Only" sourcebook covering sirens, satyrs, lamiae (the plural of "lamia"), and other creatures that attack adventurers through their libidos? If we dared to put it out, I suspect it would be one of the best-selling supplements of all time. No, no, down boy! (Sound of slapping hand in background.)
Getting back on subject, try cracking the zoology and paleontology books. There are lots of animals out there, both modern and prehistoric, that deserve heavy coverage in their own sourcebooks. How about sabre-tooths, for example? Ever since the Age of Mammals began, sabre-toothed predators have evolved independently about ten times, including at least one marsupial. Not only that, but the beginnings of sabre teeth could be seen in the ancestral reptile Dimetrodon, and virtually all of the carnivorous mammallike reptiles had at least one pair of sabre teeth (some had two or three). In addition, sabre teeth were used as defensive weapons by herbivores as diverse as herbivorous mammallike reptiles---the jonkerids, for starters---and the uintatheres that appeared early in the age of mammals. In addition, the elephant Dinotherium had tusks shaped like sabre teeth, and even today, the Indian rhinoceros prefers using teeth instead of its horn against an enemy. Oh, and today's clouded leopard has the disproportionately largest canines of any carnivore today, making its descendants prime candidates for a futuristic sabre-tooth. Sabre teeth seem to be part of the basic mammalian heritage, and we ought to be able to do something with that in a book.