kelpies...half horse half fish that will carry people off to the sea(northern europe i believe)

bunyips
Bunyips are legendary spirits or creatures of the Australian Aborigine. Bunyips haunt rivers, swamps, creeks and billabongs. Their main goal in life is to cause nocturnal terror by eating people or animals in their vicinity. They are renowned for their terrifying bellowing cries in the night and have been known to frighten Aborigines to the point where they would not approach any water source where a bunyip might be waiting to devour them.

mokele-mbembe
The mokele-mbembe is an alleged living sauropod dinosaur now living in the Likouala swamp region of the Republic of Congo (Zaire). The animal has allegedly been encountered by local pygmies who have given the creature its name. Mokele-mbembe means, depending on your source, "rainbow", "one that stops the flow of rivers", or "monstrous animal." The mokele-mbembe is allegedly the size of an elephant (the favorite prey of the local pygmies) with a very long reptilian neck. The creature is said to be hairless and reddish-brown, brown, or gray, with a tail five to ten feet long. The creature apparently spends most of its time in the water, but the pygmies claim they've seen prints left on land of a three-clawed foot.
http://skepdic.com/ticrypto.html

the kelpie i remebered myself, and like fero i have several books discussing various entities...for truly scary ones check into the ancient sumeriand and babylonian religions...now they has some powerful creatures...but i found skepdic.com an interesting site...