http://www.mangago.me/read-manga/kuroneko_kareshi_no_asobikata/ (this series)
http://www.mangago.me/read-manga/i_want_to_be_naughty/ (the whole warui series)
http://www.mangago.me/read-manga/katekyo/
http://www.mangago.me/read-manga/kokoro_kanda_neko/ (pretty smutty)
http://www.mangago.me/read-manga/himegoto_asobi/ (a bit smutty)
http://www.mangago.me/read-manga/hidoku_shinaide/ (this manga can be pretty smutty)
http://www.mangago.me/read-manga/honto_yajuu/ (can be pretty smutty)
forgot these (they're fairly known so you probably read them, but they are long and have good amounts of smut):
http://www.mangago.me/read-manga/haru_wo_daite_ita/
http://www.mangago.me/read-manga/you_re_my_loveprize_in_viewfinder/
http://www.mangago.me/read-manga/koisuru_boukun/
oops i mean smut mangas