Really, I think the Japanese are hands down the best illustrators of weird and wonderful monsters. Pink Tentacle -- one of my favorite sites for all things Japanese-bizarre -- continues to offer smashing posts on Monster Scrolls from the 18th and 19th century. Many of the monsters are not just part of traditional folk lore, but more urban myths created after sitings of these unique and creepy creatures. The first two images here are from the Kaikidan Ekotoba Monster Scroll (Kyushu) and the bottom two are examples from the Bakemono Zukushi Scroll (Edo). Do stop by and have a look at the whole scrolls. Every image has a little note of explanation which is really helpful. They really boggle the imagination which is kind of fun, though you may need a nightlight in the future.
And since we're talking ghosts and monsters and nightlights here...I couldn't resist adding this hilarious video of a Thai Light Bulb commercial. Wickedly good use of ghosts as an inducement to keep your lights on all the time!