So to wrap up Code: Black, the setting can easily incorporate source material from a variety of horror RPGs.
Fabulous Monster Hunters
Keep in mind, however, that the primary approach toward monsters in Code: Black is that -- at their core -- all these monsters are also former inmates on Prison: Earth. They're evil, and because they're not human, they tend to be more touch by Evil than humans. Of course, some humans could probably give them a run for their money; and maybe one or two are 'redeemable' by human standards. But those are few and far between. Most monsters are for killing, pure and simple. It's just that there are enough numbers of them that all out war between the monsters and humans would make things very messy, especially for those born without The Sight -- the ability to truly see things for what they are. So there's an uneasy truce, and killings are only countenanced in set rules of engagement.
Stalking the Mythos
The Laundry contributes an interesting take on the nature of the Deep Ones and the greater powers of a mythos-choked Earth, and the tenuous detente with the various occult organizations of the world. It also posits a math-based basis for magic and summoning of creatures that was explained more fully in the novels of Charles Stross. Furthermore, it gives source material on the possible structure of anti-mythos government agencies not only in the U.K., but also around the world.
Trail of Cthulhu has a plethora of adventures set in modern times that will challenge the agents of Code: Black's Brotherhood of Gilgamesh; Delta Green will give an example of a cell-structure based conspiracy of mythos-fighters in the American idiom that can be easily tweaked to avoid contradictions with the material from The Laundry.
Exploring True Reality
Kult's main proposition -- that the true reality is the city known as Metropolis, and our reality is a prison meant to keep humanity from awakening to their true nature -- is very in sync with the cosmology of Code: Black. Furthermore, the creatures and monstrosities that fill the RPG are more inspired by the Hellraiser and Nightmare on Elm Street movies and books -- and perhaps the Silent Hill series of games, which can make for a different change of pace adventure as well.
JAGS Wonderland & Book of Knots are very similar, though realized through a wonderfully dark and consistent use of the Alice novels as both inspiration and metaphor for humans dealing with the dangers of different levels of reality.
Esoterrorists tackles agents struggling to stop the breakdown of our reality, and covering up the attempts of Esoterrorists to release imprisoned intellects and entities and extradimensional realities into our own.
All in all, Code: Black is a lovely kitchen sink setting that allows GMs and players to make use of almost any horror RPG material.