I will briefly mention that Tinami and Nijie exist, but so far I have not found anything significant from either. This is bound to change eventually of course, it's just a matter of when.
http://nijie.info/http://www.tinami.com/Both require Japanese translation and an account, but that should be about as simple to handle as Pixiv or Nico Seiga.
(All of my /e/-related images from Tinami and Nijie are posted to /e/ already, so I'll just put up this nice sexy mecha.)
