I've recently read three books related to (or partly related to) that odd little subspecialty called cryptozoology. Cryptozoology, when approached scientifically, is a valid pursuit: it does, after all, deal in falsifiable hypotheses, the basic test of a science. That is, cryptozoological hypotheses can be proven false, even though the resources needed to disprove a proposition like "there is an unknown Himalayan ape species" may not be available. Some arch-skeptics lump it with ghost-hunting or chasing UFOs, which is logically unsupportable. We can never prove there are no ghosts or no visiting aliens, but we can prove (and, in some cases, have) that there is or is not a specific type of creature in a specific habitat.
A book focused entirely on cryptozoology is Michael Woodley's In the Wake of Bernard Heuvelmans (CFZ Press, 2008). The title comes from Heuvelmans' book In the Wake of the Sea-Serpents and examines several alternative schemes used by that author and others to group sightings of large unknown marine animals in ways that may point to a particular type of creature. Although such a study is necessarily incomplete with no actual creatures to examine, it does have value as an intellectual exercise to help focus our thinking on the subject. Woodley summaries theories about "sea serpents" in general and goes through Heuvelmans' classifications, the types of creatures that might be behind them, and the way other researchers have classified the same types of reports (as Woodley acknowledges, Heuvelmans' bestowing of scientific names on creatures with no type specimens is invalid, although he uses some such names for convenience). Woodley offers thoughts on the plausibility of of Heuvelmans' types and suggests modifications to his categories. The whole effort is well written, although I have some quibbles about what cases Woodley thinks are worth including. The report of the ship Pauline, which describes a huge serpent wrapped around the body of a sperm whale, makes no sense as zoology - no eel, frilled shark, or other elongated marine creature is a constrictor, and there's no reason to think a giant form would be. I would toss this report aside as either a fabrication or a very confused sighting of a giant squid/whale battle. Another is the story from the German submarine U-28, which many cryptozoological researchers (of which I am one) dismiss. Still, the point of this book is the big picture, not the individual reports, and from that perspective Woodley's book was well worth my time.
Ken Gerhard and Nick Redfern's Monsters of Texas (also from CFZ Press) is a fun read, setting down reports of giant birds, sasquatch-type things, and other Texas oddities, The authors present what people have claimed in a straightforward fashion, leavened with humor though applying a little less skepticism than I would have used. Their most important contribution, I think, is documenting that there may be a grain of truth hidden in the chupacabras myth, since coyotes and coyote hybrids with long hind legs, prominent fangs, and hair loss seem to turn up in Texas often enough to hint there may be some recurring genetic anomaly presenting itself.
The authors do take with some seriousness stories of zoologically impossible or improbable things they think may be apparitions, and these turn up a lot more in Redfern's book Memoirs of a Monster Hunter (New Page Books, 2007).
This book mixes topics I normally wish writers would not mix. I don't automatically dismiss as nonsense the accounts of people who think they've seen non-physical entities - it's a big, strange universe, and there's a lot we don't know about how the human brain perceives and responds to different phenomena. To me, though, poking into such topics is parapsychology, not cryptozoology, and including the two in any book makes the cryptozoological part (or the whole book) more likely to be dismissed by those trying to think scientifically about real animals. Of course, Redfern has written a memoir, and thus is entitled to include everything he has investigated that he personally believes has some basis in reality. He writes with characteristic humor and spins a good tale. His accounts of his adventures filming TV shows are especially fun.
I found myself sometimes thinking, "Wait, you needed to think some more about that." When Redfern visits a spot where a weird two-legged creature has been reported and finds a tepee-type arrangement of broken branches, he connects it to similar reports by others investigating Bigfoot and never seems to consider that normal human kids build such structures (I remember doing it myself), and whether an area is supposed to be open to visitors or not may not make any difference.
So that's my take on these books. All could have done with better bibliographies, and the last two are not skeptical enough for the science writer in me. (I have no special training or other claim to monopolize the term "science," so I will admit others may read things differently.) But I had a good time reading these and learned some things. So thanks, folks.