Reddit reviews xxxHOLiC: AnotherHOLiC: A Novel

I read them in Japanese, but some of his novels have been translated into English:
http://www.amazon.com/dp/0345505182/
http://www.amazon.com/dp/142151883X/
http://www.amazon.com/dp/0345504275/

As for anime, there are two other series:
http://myanimelist.net/anime/6594/Katanagatari
http://myanimelist.net/anime/11761/Medaka_Box

Zaregoto: Book1 and Book 2, Death Note: Another Note, and XXXHolic: Another Holic from the best mystery author IMO, NisioisiN


Also note, that NisioisiN is the author of the monogatari series (Bakemonogatari, Kizumonogatari, Nisemonogatari, Nekomonogatari, Kabukimonogatari, Hanamonogatari, Otorimonogatari, Onimonogatari, Koimonogatari, Tsukimonogatari, Koyomimonogatari, Owarimonogatari., Zuko-Owarimonogatari, Orokamonogatari, Wazamonogatari)

There are a lot of mystery/horror novels in syosetu.com, it's just nobody translates them, just like there are a lots of BL novels that aren't translated

EDIT 1: I would like to add Ballad of a Shingami series

EDIT 2: .Hack// Another Birth series

EDIT 3: Utsuro no Hako to Zero no Maria