Yamada Gouki (山田剛毅), aka goking, has been illustrating creatures from the Cthulhu Mythos and similar horrors in an ukiyo-e style: Cyaegha, Igolnaku, The Thing That Plays with Fate, Cthonian, Byakhee, and would like to wish you a very Merry Fishmas from Innsmouth. You can find more illustrations on his Twitter or his blog, 2D6. [more inside]
Illustrator Jed Henry and woodblock printmaker David Bull recently collaborated on a set of videogame-inspired woodblock prints in the ukiyo-e style. Just recently funded through Kickstarter, the prints are already underway. There are videos of the creative process here and at the bottom of the first link.
Tokyo artist Sagaki Keita creates incredibly detailed illustrations which are almost completely improvised. More of his work can be found on his website.
Old anatomical illustrations that provide a unique perspective on the evolution of medical knowledge in Japan during the Edo period (1603-1868) [more inside]
Weirdly wonderful illustrations from 70s Japanese children's books by Gōjin Ishihara, including much nightmare fuel from the Illustrated Book of Japanese Monsters
Yōkai Daizukai is an illustrated guide to yōkai authored by manga artist Shigeru Mizuki. [more inside]
Japan's National Diet Library Gallery has been mentioned here before, but the Pink Tentacle blog came across some fantastic late Edo period illustrations in the NDL Gallery by Kurimoto Tanshu (栗本丹洲, 1756 - 1834). Apparently he was a doctor, but he seems to be better known for his hundreds of biological illustrations. Many are of sea creatures, but there are also quite a few other plants and animals. ranging from realistic renditions to bizarre creatures. A huge and varied collection, but all are equally fascinating.
Kodomo no kuni - children's book illustrations and songs from 1920s Japan. I found the artist's index the best way to navigate. (via the always entertaining quiddity)
Funky Radical World was created by Japanese illustrator Radical Suzuki - don't miss the delightful fashion show. One of my favorite works is Real Tokyo Girls, a flash animation about the rather fascinating Ganguro girl fad. This gallery includes a few more samples of his work. warning - some cartoon nudity may be involved!