If you're looking for manga similar to Koi Neko, you might like these titles. All recommendations are made by Anime-Planet users like you!
One day, a ronin student on his way home gave a bentou to a cosplay cat girl. Unexpectedly, the cat girl then decided to stay at his house, resulting in the two living together. But then, the girl turns out to be one of the mountain shrine's Gods. Having to deal with the girl’s magic plus the teasing from other cats and Gods keeps the main character’s hands absolutely full. Will he ever get a break or will this “big pet” burden him forever?
In both manga a cat was turned into a catgirl and now pesters some guy. In both manga the catgirl has common sense of a cat. As a whole, Koi Neko is the better one, because the jokes are funnier and there is actually some romance there. Nonetheless, if you liked one and are looking for more, the other manga might be the thing.
After spending half a year abroad, Kinosaki Yuichiro is in for a shocking homecoming when he discovers that his inventor/scientist father has given his 3 dogs the appearance and abilities of girls. Now he is in for a ton of grief as he tries to cope with these changes.
It's guy bothered by doggirls in one and guy bothered by catgirls in the other. In both series (at least) one of the animal girls is head over heels in love with the mentioned guy. I found Koi Neko to be much better of those two, but I guess they are kind of similar, so if you liked one, you might try your luck with the other.
P.S. Koi Neko has very little fanservice, but Inumimi isn't exactly "lacking" in that aspect, so keep that in mind.
Long ago a magical cat disguised as a human woman fell in love with a human man. It is said that during their time together they even had children. They say that afterwards, the magical cat dwelt happily as a human, that she ascended to the heavens and became a cat-god, and is even now watching over the world of cats and men. Of those descendants, the cats of Cat Forest Town say that they have mysterious powers. The townsfolk care for the cats as their guardian dieties, and the cats, too, have become attached to the humans.
In both manga male lead is pestered by a bunch of catgirls in love. The catgirls happen to be actually (major plot twist) cats. The cast also gets joined by a cat-loving girl which makes those two series even more similar. Note that Tamanyan is considerably ecchi-er and more haremy than Koi Neko, which in comparison manages to balance comedy and romance nicely and is generally low on ecchi. Nonetheless, if you liked one of those two manga and want to read another in which cats turn into girls, then the second one might fit the bill.