"Evil" humanoids? What makes the Evil? The fact that some guy named Volo walked by some tribe of them one day and saw them doing something he didn't understand, and didn't stick around to learn about the deep and meaningful values of their community? If anyone is evil, it's those darn "adventurers" who keep breaking in to completely innocent monster's homes! *this message paid for by OGRE (Orcs for Greater Respect Everywhere)
Seriously though, I really don't like running "evil" races. I'll run evil tribes, evil cultures, evil kingdoms but running evil "races" just bugs me too much on some fundamental level. So typically:
Orcs are warriors, they practice ritual blood sacrifice to their gods and believe peace is a lie and only through battle and strength can one achieve "enlightenment. They're more violent and aggressive than Klingons, but less structured. There are dozens, if not hundreds of different orc tribes, some ranging from a few dozen members to several thousand. Each one with their own minor variances. Every once in a while some great leader unites them, wages a brutal war against the rest of the world, then their rag-tag unity falls apart.
Kobolds aren't evil, they're just dumb and typically poor. They're more or less sentient rats in my world. They're so universally looked down upon by other races that they steal and raid food supplies out of necessity. They're incredibly short lived. An "old" kobold is roughly 20 human years. Few kobolds make it past 10. They have a simple religion revolving around the chromatic dragons as representations simple concepts within the natural world, earth, nature, death, etc....
Gnolls are probably the most "inherently" evil race, but mostly because again: they're dumb, they're despised and they mostly worship a psychotic monster-demigod who warps their minds and bodies into savage and violent forms. There are much less violent gnolls, they're still dumb and despised and poor, but they worship various nature gods or anything that won't turn them into savage killing machines.
Goblins are somewhere between Orcs and Kobolds, they're like the Orc's dirty, poor, stupid, ugly cousins. They steal, raid, pillage and murder because they really aren't capable of building a society that the nearest group of Orcs, Elves, Humans, Dwarves or any other race that wants their land comes in and kills them.
Hobgoblins are essentially the same as the orcs, but much less shamanistic and with a much more "organized" sort of approach to warfare. They have a much more structured society and adhere to a more formal code of laws. They believe in very hard justice, very strict codes of honor and very organized lives. A Hobgoblin almost always has to be somewhere to say prayers, go on a hunt, practice warfare, as they have found that the less structured a Hobgoblin's life, the more like Bugbears they become, dumb, primitive and bestial. Few other races visit Hobgoblin cities as there are simply so many codes and rules to follow, all with a variety of painful punishments, strangely, none of which are death.
Bugbears are the Hobgoblins big, ugly, stupid cousins. They're barely intelligent, but they're so powerful they get more respect from the more sentient races, unlike the kobolds. They operate on a primitive loose tribal basis. They band together as things endanger them in a given area and fall apart when things get quiet. They tend to wander over great distances in their lives.
Minotuars are like if Gnolls and Orcs had an angry baby. They worship a crazy god of war and bloodlust who of course, warps their body to make them more savage and bloodthirsty. They have a more organized society than Gnolls, but are less civil than Orcs. Believing their god unable to manifest on the material plane because he was trapped in a extra-dimensional maze, Minotaurs abohor construction. Even in the most intolerable of conditions a Minotaur will prefer to be outdoors, unfettered and unrestricted by a wall or a roof.
Trolls are like Bugbears. They're not highly intelligent and they have small tribal groups where they do very primitive tribal sort of things. Otherwise they are essentially hunter-gatherers, and you fight one usually only because you intrude on their hunting grounds. They're moderately more intelligent than Bugbears, but most people couldn't tell you how.
Yuan-Ti are probably the most civilized "monster" race just below the Drow. They obviously worship a crazy snake god, but unlike the Gnoll or Minotaur gods, the Yuan-Ti must earn their blessing, much like the Drow. Every Yuan-Ti has minor snake elements. The hybrids are all "blessed" by their god and given a purpose in society. Yuan-Ti society is insanely structured and heavily caste-based. Not all hybrids automatically outrank purebloods, as the Yuan-Ti are highly respectful towards skill and encourage it in warfare, art, literature and every aspect of life. Hybrids only usually outrank purebloods due to the fact that they earned their blessing because of their skill, many think the reverse is the case. Punishment in Yuan-Ti society is simple: their "snake blood" is removed, rendering them essentially, humans. Then they are exiled.
Drow are of course, just as civilized as their various cousins, but their society revolves around a very strong "cull the weak" manifesto, but at the same time, killing for the Drow is literally an art. Murdering someone in a back alley is still bad, unless of course you make it into a powerful artistic statement or tribute to Lolth. Hearing that someone has "disappeared" is common, but it's unlikely you'll ever hear of an actual murder, since murder is a-okay provided you're of the right caste, your target showed weakness or Lolth said so. There are two kinds of Driders in my Drow society. The "sexy human on top"-spider lower half, and "monstrous" Driders who lack almost all human physicality. The former are blessings to Lolth's faithful. The latter are punishments, or jokes, or boredom, ah...the joys of a psychotic spider-goddess.
Illithids are aliens. Pure and simple. They are, by best comparison, like the aliens from Independence Day, they move through the aether until they find a suitable world, and start to convert it (through essentially magical terraforming) to a world of their preference, while feeding on the native intelligent populations. They then reproduce, strip the world of it's useful elements, leave and repeat. All Illithids are exactly as ranked as every other Illithid, their minds are magically linked to each other across the aether. There are no secrets between them, and what one knows, they all know...provided their link is not severed, though that usually drives an Illithid insane. The Illithids are something of a cross between the Borg and the Wraith. The Illithids are surprisingly atheistic, due to their vast knowledge, they understand the most "gods" are simply very, very powerful, very ancient beings and that worship feeds the gods, therefore no religion.
Most "non-monstrous" races simply disagree with these creatures code of ethics, religion or concept of morality, in the same way that elves reverse nature and are often disgusted by human disrespect, or dwarven "digging".
