I read back through the Grimoire thread looking for these and didn't find them, but it's late so maybe my search was... lame? Anyway:

From Falderal over at Bungie.net:

Ghosts

"In its dying breath the traveler created the ghosts... to seek out those who can wield its light as a weapon, Guardians that protect us and do what the traveler no longer can."

Built from machinery and the travelers light, Ghosts guide their guardian companions in the quest to reclaim our solar system. Every ghost seeks out its guardian among the ancient dead, the ghost serves as a scout, librarian and mechanic, waking ancient machinery and cracking ancient codes, Ghosts can even save a guardian from death. But ghosts are not immortal, every loss is irreplaceable.

Human

"This was our world, our solar system. We were here first. And no matter what the darkness brings, we will be here when it dawns."

Humans are survivors, tough and resilient, descending from those who built a golden age only to see it ripped away. Now, after an age of retreat and desperate struggle, they fight to take back their solar system and claim a new future. Their are those who believe the traveler choose earth for a reason. Now it is humanities obligation to prove themselves worthy of its light.

Awoken

"The others sing the song of light and dark. We together have transcended such unimaginative limitations."

It is said the awoken were born in the Collapse, descended from those who tried to flee its wrath. Something happened to them out on the edge of the deep Black, and they were forever changed. Today many awoken live in the distant reef aloof and mysterious, but others returned to earth, were their descendants now fight for the city. Earthborn awoken sometimes venture out to the Reef, hoping to learn its secrets - but find no special welcome form the reclusive queen.

Exo

"Ask yourself, what threatened your Golden Age ancestors so much that they built the Exo to defend them"

Built for a long forgotten war, the Exos are self aware war machines so advanced that nothing short of a ghost can understand their inner functions. They remain ciphers, even to themselves, their origins and purposes lost to time. Whoever built the Exos fashioned them in humanity's image, gifting them with diversity of mind and body. Many of the Citiy's Exo citizens work and live aside their organic brethren. But others fight again, re-forged in the light of the Traveller to serve as guardians.

And yeah... if everybody but me has seen these before... well... tough. :p