A thought experiment.
Theory: Though originally inspired by Tolkien's work, D&D and Pathfinder have selected physical characteristics of what may be considered to be the "major races" of a given campaign setting based on a select few traits. In addition to the standard PC races we are familiar with, excluding humans and hybrids, the choices of common villainous races (which also serve as alternate PC races for some) serve to "fill in the blanks," as it were.
The primary characteristics in question are:
(a) Height,
(b) weight/build,
(c) Morality, and
(d) Hairiness.
These four traits can be mapped to a table of boolean attributes.
Height: {tall | short}
Weight/build: {light | heavy}
Morality: {good | evil}
Hairiness: {hairy | nonhairy}
Mathematically, these four boolean traits allow for up to 16 non-human non-hybrid races. This does not exclude the possibility of making each of these races more distinct by giving them additional traits unrelated to these four basic characteristics, for example giving dwarves stonecunning, or giving elves resistance to enchantment magic.
Here's the breakdown:
Race = (CODE) = (Height) (Build) (Morality) (Hairiness)
Kobolds = 0000 = short, light, evil, nonhairy
Goblins = 0001 = short, light, evil, hairy
? = 0010 = short, light, good, nonhairy
Halflings = 0011 = short, light, good, hairy
Derro = 0100 = short, heavy, evil, nonhairy
Duergar = 0101 = short, heavy, evil, hairy
Gnomes = 0110 = short, heavy, good, nonhairy
Dwarves = 0111 = short, heavy, good, hairy
Drow = 1000 = tall, light, evil, nonhairy
Gnolls = 1001 = tall, light, evil, hairy
Elves = 1010 = tall, light, good, nonhairy
Satyrs = 1011 = tall, light, good, hairy
Hobgoblins = 1100 = tall, heavy, evil, nonhairy
Orcs = 1101 = tall, heavy, evil, hairy
? = 1110 = tall, heavy, good, nonhairy
Centaurs = 1111 = tall, heavy, good, hairy
Of course, a few iconic virtuous and villainous races will inevitably be missed: aasimar, bugbears, ogres, and troglodytes, just to name a few. Certainly a fifth meaningful attribute could be added that might accommodate these and other races remaining in the Advanced Race Guide to expand this table further.
The table above has two significant gaps:
the short-light-good-nonhairy race (SLGNH), and
the tall-heavy-good-nonhairy race (THGNH).
It could be argued that D&D/PF halflings are in fact the SLGNH race, but this only leaves us with the problem of figuring out which race is the short-light-good-hairy race (SLGH).
Now, if you care to depart from established lore, you might have Hobgoblins as a good-aligned or "redeemed" goblinoid race, which will let you fill the tall-heavy-good-nonhairy (THGNH) slot, and allow you to place troglodytes in the tall-heavy-evil-nonhairy (THENH) slot.
That's all I got. Your thoughts?