Odd, I could've sworn I posted in a thread like this earlier...
I'll put a less comprehensive version of it (Sources only, no source finding/source browsing) just for you though.
My number one source of images is Pixiv (
http://www.pixiv.net). Pixiv is a fantastic art site for pretty much anything, it's very conservative but has an excellent community. A majority of the tags are in Japanese though, so you'll need a bit of translation/searching to get it right. Also note that Pixiv is a revolving door - what's up today may not be up tomorrow.
Second place is best described as "miscellaneous" - developer blogs and official sites, fan galleries, artist blogs and galleries. Listing them would be pointless, but in general Danbooru (
https://danbooru.donmai.us) has a good listing of such in their artist and source listings. Note that Danbooru itself has pretty much no original content.
Third place is probably Nico Seiga (
http://seiga.nicovideo.jp). Static image portion of a Japanese video site similar to YouTube. Again, tags are mostly in Japanese, so you'll need translation tools and such.
Fourth would be Nijie (
http://nijie.info). Japanese tags yadda yadda, also while the site has a fair deal more smut than what /e/ would expect there's certainly more tame things on it if you look hard enough.
Fifth would be deviantART (
http://www.deviantart.com). I generally only go for artists I love and stick to them, since frankly the quality-to-crap ratio on dA is much, much lower than on Japanese equivalents such as Pixiv. The ads can be annoying, too.
As far as I know it's not a site that hosts porn but I also have content from Tinami (
www.tinami.com) that just barely qualifies as erotic. Much like Pixiv, from what I can tell.
