Petshop of Horrors is excellent; it's a pitty only four of the stories were animated.
elemental user: Petshop of Horrors is about a man/mysterious being named D who runs a pet shop out of China Town. He'd sell unique animals/creatures to people, offeriing to fulfil their dreams but often destroying them instead. A "rabbit" that looks exactly like a bereaved couples dead child, a mermaid in the form of a client's fiancee, who killed herself when she found him with another woman ... (both those stories are in the anime).
The two other main characters are Leon Orcott, a police officer who correctly suspects D of being involved with a series of strange deaths (a burnt out actor is found dead in his appartment, along with a strange lizard... a gangster is found dead, apparently torn apart by wild animals in the middle of the city...), but who eventually grows quite close to D, and Orcott's little brother (not appearing in the anime), a mute boy who can communicate with D's animals.
A warning, though: the author of the manga is apparently an environmentalist, and even I, who agree with him, think he gets pretty heavy-handed sometimes. Still very good.