Fantastic Noir

"The Butler Did It! With a death curse! From space! Take him away, Troll Patrol!"

A sister trope of "neo noir" or Cyberpunk, fantastic noir is a relatively small Subgenre that blends the setting, characters (it usually stars a Hardboiled Detective) and plot structure of a Film Noir mystery story with the more colorful elements of Fantasy and Science Fiction. The genre seemed to arrive all at once in The Eighties and remains strong today, with the publication of such books as Anonymous Rex, Who Censored Roger Rabbit?, and The Hollow Chocolate Bunnies of the Apocalypse.

Examples of Fantastic Noir include:

Film

Cast a Deadly Spell. Phillip Lovecraft is a detective who doesn't use magic in a world where everyone else does.
The Animatrix short "A Detective Story".
Who Framed Roger Rabbit?.
Preeminent on the SF side, Blade Runner.

Literature

Stalking the Unicorn by Mike Resnick. A private detective is hired by an elf to find a missing unicorn.
Who Censored Roger Rabbit? has human detective Eddie Valiant solving crimes in a world where cartoon characters are a living, breathing people (some of whom happen to work in comic strips, television and movies) discriminated against by the more numerous humans.
Anonymous Rex. The detective Vincent Rubio is a velociraptor in a world where dinosaurs aren't dead but hiding.
A Study in Emerald. Sherlock Holmes isn't noir, technically speaking, but this short story is a near-perfect snapshot of this subgenre.
Nursery Crime blends fairy tales with a Police Procedural / 70's-style Cop Show aesthetic. To a degree, Thursday Next qualifies, too.
Many of The Dresden Files books — especially the earliest ones. Hard-boiled detective monologue running smack up against wizards, faeries and vampires. Results in many tons of awesome.
Glen Cook's Garrett P.I..

Tabletop Games

Eberron is geared towards that kind of play, amongst others. Even including a prestige class for it.

Video Games

Thief
Discworld Noir (a more humorous take on the entry, as you'd expect from the source material)

Web Comics

Problem Sleuth mixes this with a World of Chaos and a flavorsome combination of awesome and weirdness.