If by "obscure" you mean lesser known creatures i can name a few. The Ziz (The thrid and lesser known counterpart to Behemoth and Leviathan) The Manticore The Cockatrice The Wyvern The Griffin or Gryfon (Spelling varies) The Nymph The Gnome (Not the Travel Gnome) Salamanders (Which turned out not to be mythical after all) The Sphinx Some that are a little more common but still a little ignored are: Cyclops' Pegasus Longs Unicorns Harpies Sirens Phoenix Giant Animals that talk
Peri - descended from fallen angels Barghest - a dog with huge teeth that comes out at night. Ichneumon - somewhat akin to a mongoose Brownie - where I assume Rowling got the idea for house elves. An invisible house goblin that would disappear forever if you tried to compensate him for his services.
I totally just remembered: Imps, the mischivious little devils (Gerlims work too if you like little furry friends )
Gremlins, goblins, other asorted fairy/fae creatures. I mean the original, rather malignant set. As for the others, I've heard/knew of most of them. Hmm, now that I think of it, Sirens. The singing to lure men to their death, though from memory it was sailors.
Jorge Luis Borges wrote an illustrated dictionary of obscure mythological creatures. It may even be called... "Mythological Creatures." But I don't remember. Anyway, it's entertaining. I'd get out my copy and try to find some for you, but my dog chewed it up.
I wish someone would turn thier back on the usual wise stargazing fantasy centaurs and make a return to the lecherous wino's who couldn't hold their drink that were the Centaurs of greek legend.
There're some good ones already posted here, and some other lesser known ones can be found at http://www.monstropedia.org. Be warned, the navigation on that page can be a little tricksy...