Loren Coleman is the world's greatest living cryptozoologist. For decades he has conducted research, written books and investigated zoology's greatest mysteries. He currently runs the International Cryptozoology Museum in Portland, Maine-- the only such institution in America. Mr. Coleman's blog is a must-read for any crypto-fan.
The Loch Ness Giant Salamander
The first time I read this blog, it completely changed my views on lake monsters. At first, its thesis seems implausible. But the author presents the most compelling and best-researched argument I have ever read in this field. His posts are long, but all are brilliant and worth your time.
Theoi is the best mythology site out there. It has entries on every god, hero and nymph in Greek myth-- no matter how obscure. The bestiary is especially impressive; it includes not only a complete list of Greek monsters, but a complete list of sources describing each one.
Karl Shuker is another of cryptozoology's greats. His blog is excellent, and doesn't solely focus on undiscovered beasts-- its nature articles are just as interesting. ShukerNature is incredibly deep in terms of content-- Dr. Shuker has written hundreds of posts since 2009, most lengthy and well-researched.
Cryptomundo is a great source for less-scholarly cryptid news. You wanna read thoughtful articles on the identity of Nessie? There are better blogs for that. But if you want to hear about the latest bigfoot sightings and movies, give Cryptomundo a try.