Oof. Where do I start? Lessee... I ran for about a year a homebrewed game that took place during the age of dinosaurs. Almost all of the sentient races were reptilian, so I had to tweak existing flavor quite a bit.
Kobolds: Kobolds are the Empire. They rule over the southern continent of Gondwana with an iron fist, collecting punitive taxes from their various vassals and conscripting them to fight their wars. Kobolds love bureaucracy in all its forms, and have a highly regimented society riddled with various minor officials. Kobolds are obsessed with genealogy, and keep rigorous track of their bloodlines. They are especially proud of devilish or draconic blood in their lineages, and marriages with fiends and dragons are often used to cement alliances between kobold families and their supernatural benefactor.
Kobolds hate the sun, and so live underground in vast artificial caverns. They raise a variety of fungus, vermin and giant subterranean lizards for food. Religion is of middling importance in kobold society--all kobolds pay lip service to Kurtulmak, their creator, but devote little attention to godly matters. The exception comes from worshiping deities not sanctioned by kobold society (Kurtulmak, various archdevils, Tiamat); these heretics are usually swiftly put to death.
Troglodytes: Troglodytes are a corruption of lizardfolk stock, the result of demonic influence and the genetics experiments of the serpentfolk. If the kobolds can be said to rule Gondwana(which they will often, and loudly, proclaim), the troglodytes are the counterpart rulers of the northern continent of Laurasia. Troglodytes are wasteful, savage and loving of filth, and much of Laurasia's once proud plains and forests now lie in ruin.
Troglodyte society, such as it is, is a violent theocracy. Conflicts between troglodytes are common, even welcomed, for a weak individual murdered is one less burden on everyone else. Demon worship is the state religion--most troglodytes passionately venerate Lagozed, as his immortal half-trog son is the undisputed Hegemon of all troglodytes. A recent trend has been towards a debased form of druidism, devoted to remaking the whole of the continent in the troglodytes diseased, corrupted image.
Lizardfolk: The lizardfolk live in mangrove swamps, island chains and marshes throughout both continents, and in the vast network of islands and shallow seas between them. Lizardfolk are shamanic, druidic, tribal people, with no interest in conquering continents or spreading their religion. Lizardfolk generally want to be left alone.
The god of the lizardfolk, Semuana, is essentially the personification of natural selection. Its only tenet is "survive and multiply", which the lizardfolk take to heart. Lizardfolk have no dietary taboos, consuming other sentients and even committing cannibalism with impunity. Lizardfolk are also intensively competitive amongst themselves, yet despite this ambition, they have no desire to expand their territory beyond their marshes and mangroves. Perhaps some ancient lizardfolk empire once existed, only to be destroyed by hubris and lost to memory.
Firenewts: The firenewts are an odd offshoot of lizardfolk blood, native to the large volcanic island continent of Surtsey. Despite their adaptations to the heat, firenewts still love the water, and most of their settlements are on the coast (this is also probably due to Surtsey being a barren desert of obsidian shards and ash fields). Firenewts eat mostly fish, although they grow some crops on what ashy soils are wet enough to be fertile. They are a mercantile people, trading metal goods and gems coughed up by the volcanoes for wood to build more boats.
Firenewts are among the most democratic of the races, having a parliamentary system complimenting a mostly powerless monarch. Firenewts as a whole are often irreligious, but a growing influence on their society is the Order of the Black Flame, a cult devoted to Bazim-Gorag, a slaad lord of fire imprisoned under the island whose rage is responsible for much of the volcanism on Surtsey.
Thri-kreen: One of the few races native to Gondwana untamed by the kobolds, the thri-kreen are mortal embodiments of chaos. The basic unit of society is a nomadic extended family, but thri-kreen often come together in conglomerations that treat the trappings of society as one huge game in which all of the rules change constantly. The only standard is that one thri-kreen (usually the strongest, the smartest or the best hunter) each year assumes the role of "Grand General", the only position of authority, who dictates the rules that society will operate by for a time.
Thri-kreen are violent, being both carnivorous and convinced that they are the only truly intelligent life. They raid settlements and caravans of other races for both food and goods, and will often "trade" by stealing goods they want and replacing them with useless rocks, garbage or even items deemed offensive by the culture in question. A thri-kreen will never willfully harm another thri-kreen, but other races are fair game. They are skilled at crafting crystal into weapons and are often psionically gifted.
Ogres: Dubbed "big-bigs" by the kobolds, ogres were until recently thought to be nothing more than mythical monsters. Recent expeditions into deep within the earth, however, have discovered that ogres do exist and are easily exploited by the more intelligent, magically gifted kobolds.
Ogres are large insectile creatures with four arms (I used the insectile template from Savage Species on my ogres). Their society is crude and primitive, with a rough hierarchy of "might makes right". Ogre morphology is highly unstable, and alpha ogres, perhaps infused with magic by the fear and beliefs of their lessers, often mutate. Both male and female alpha ogres grow sharp teeth and horrible rending claws, but male alphas gain amazing regenerative properties, whereas female alphas gain magical powers and skin like iron.
(I used insectile trolls for male alphas and insectile annis hags for female alphas).