I like non-human races. I understand that isn't a common opinion in the OSR; I read lots of blogs and campaign settings that are human-only or at the least human-centric. One could argue that OD&D was human-centric since it placed harsh limits on demihuman characters. (Halflings could advance only to 4th level and only as fighters, essentially) I present a few optional races for the Mythic West.
CACTOID (Inspired by RIFTS, and I'm not even sorry)
Cactoids appeared shortly after the the flood of magic from the West. Some cacti in the Southwest animated, having gained sentience. Cactoids have since spread out across the country.
A Cactoid is humanoid, but with a hard, plant-like skin covered in thorns. They have pitch black eyes and speak in warbling, distorted voices through a mouth cavity. Cactoids stand 6-7 feet tall. They are genderless, producing by flowering and depositing seeds. They tend to live in small, village-like communities, though some have attempted to integrate into human society.
Cactoids may advance as Trailblazers or Magicians. They are limited to 6th and 4th level, respectively.
Hardy: Cactoids have +2 to saves against disease or poison. This is cumulative with any bonuses granted by character class.
Plant: Cactoids have no need for human food. Daily exposure to sunlight (even overcast) is enough to nourish them. Cactoids who spend too much time underground are subject to starvation. Magical light, such as that from a spell, will nourish them. Artificial light will nourish them, but they are at -1 to attack and save until they get some natural or magical light.
Thick Skin: Cactoids receive a permanent +1 bonus to Defense due to their thick hides.
Thorns: A Cactoid's unarmed attacks inflict +1 damage. In addition, anyone making an unarmed attack against a Cactoid automatically takes a point of damage.
DEVIL-KIN (Inspired by some monster from Dark*Matter that I only half-remember)
Devil-Kin are a race of mortal humanoids who come from a hellish dimension parallel to ours. (Or perhaps they're actually from Hell) They stand between 6 and 6 1/2 feet tall, with narrow limbs and slight frames. They have thin, bony features, usually a prominent chin and nose. They have pointed ears and tiny horns growing out of their foreheads and pointed, vestigial tails. Their skin coloration may be shades of red, violet, or blue. The hair of a Devil-Kin will be jet black, firetruck red, or a blue-black. Males favor goatees.
Devil-Kin are often mistrusted or outright shunned by polite society, so many end up on the wrong side of the law.
Devil-Kin may advance as Shootists (to a maximum of 4th level), Gamblers, or Magicians. (They may progress to the 6th level in the latter two classes) They may also choose to advance in a dual-class nature as a Shootist/Magician or a Gambler/Magician. If this is the case, the Devil-Kin chooses which class to play at the beginning of each adventure. Dual-classed Devil-Kin keep experience totaled separately, and only earn half-experience points from adventures.
Evil Heritage: Devil-Kin can be banished by Preachers. They are compelled to flee as undead. The HD of the Devil-Kin is equal to his experience level. If dual-classed, use the level of the class that the Devil-Kin is currently operating as. In addition, holy water inflicts 1d4 damage if splashed on a Devil-Kin.
Magic Resistance: Magical energy directed at Devil-Kin seems to bend and twist around them. They receive +2 to all saving throws vs. magic. This is accumulative with any bonus from character class or other sources.
Silver-Tongue: Although mistrusted, Devil-Kin have a semi-magical ability to win people over. Once per day, they can cast a charm person spell, disguised as a suggestion, flurry of flattery, or some similar exchange.
These are small, dwarf-like beings, ranging from knee-high to waist-high on a human. Different Native tribes have different names for them, but all refer to the same species of being. (White Americans probably think of these creatures as dwarfs, fairies, pixies, etc.) Different families/clans of these creatures often have a particular feature unique to that region: one eye, flat faces, impressive beards, etc. Even the name is something of a misnomer; many families live in forests, but some dwell in hills or caves or near rivers.
Forest Folk are permitted to advance as Gamblers, Magicians, or Trailblazers. They may advance as high as 4th level in those classes. A Forest Folk may switch classes at 4th level, starting over at 1st level. They retain their hit point totals and abilities, but only gain half experience. A character must have a Constitution of at least 9 to be a Forest Folk.
Nearly Invisible: Forest Folk can hide in the woods on a 1-5 on a d6, and a 1-3 in other natural surroundings. They have the same chance to move with near-absolute silence. These abilities can only be used if they are alone, unobserved, or only in the company of other Forest Folk.
Small Stature: Humans and human-sized creatures suffer a -2 penalty to hit Forest Folk due to their tiny size and tricky nature.
Throwers: Forest Folk have an uncanny knack for attacking with thrown weapons, receiving +2 to their attack rolls made with such. In addition, even a small rock will inflict 1d4 damage when thrown by a Forest Folk.
Variant: If you like, and have access to a S&W version of the Druid class, Magician Forest Folk use the Druid spell list instead of the Magic-User spell list.
(This class was built off the White Box Halfling, flavored by entries from various Native American myth websites.)