Most of the races in Eberron have the same general flavor as the standard one, but there are enough exceptions that it’s worth giving a quick run-down. In addition, dragonmarks are race-specific, so I’ll note which have which.
Humans: Humans are, as usual, the majority race and run most of the kingdoms created as a result of the Last War. Humans can have the Mark of Finding, the Mark of Handling, the Mark of Making, the Mark of Passage, and the Mark of Sentinel.
Half-Elves: Half-elves, also as usual, are kind of ill-defined and are basically humans with pointy ears. But they do have two cool dragonmarks: Detection and Storm.
Half-orcs: Unlike the vibe in standard D&D, half-orcs in Eberron are the remnants of an ancient empire. They tend to be primitive but in a noble-savage kind of way: many are druids, and it was only through their efforts that an incursion by weird creatures from another plane was fought off centuries ago (too bad nobody besides a few druids still remembers this). Some half-orcs these days live in the frontier kingdoms, living a prospector’s or trapper’s lifestyle: this is made easier for them because they can have the Mark of Finding.
Halflings: There are two kinds of halfings in Eberron. There are the ones that live in the cities. These are pretty similar to standard D&D: some are a little rogueish and sneaky, some are nice and hospitable (the second type is even the more common, as their marks of Healing and Hospitality let them run inns and waystations). Then there are the wild halflings. They live out in the desert, tame dinosaurs to ride, and are masters at setting up ambushes for their prey. Yeah. So before you mess with a halfling, better find out how long it was since he came from the desert.
Gnomes: Gnomes in Eberron look short and cute and big-nosed and adorable, just like in standard D&D. They make themselves useful at banks and libraries and museums with the Mark of Scribing, and hardly anyone thinks an unkind word about them. Which is just how they like it. Because you know how the Gnomes of Zurich live in Switzerland and are the Illuminati-like secret masters of the world through their control of finance and agents in every government and organization? That’s these guys. The tiny gnome kingdom of Zilargo is thick with conspiracy, treachery, political maneuvering, and backstabbing. Outsiders who come in are unlikely to see any of it, and just go away thinking how clean and safe all the streets are. But that doesn’t mean it’s not there. Oh, the gnomes are also masters of elemental binding, so they have enormous political leverage by being the only ones who can power the airships to make those fly (although it takes a half-elf with the Mark of Storm to steer one).
Elves: There are basically three kinds of elves in Eberron. There are the ones with the Mark of Shadow, who belong to either of the two guilds that specialize in entertainment, storytelling, acrobatics, music, and spying. There are the ones that live on Aerenal, the island over the sea, where they are rumored to be ruled by an Undying Court of the most revered ancestors — or perhaps this is just rumors caused by their reverence of their ancestors, study of history, and obsession with death. Finally, there are the crazy warrior elves, who decided to stake out a claim on the main continent for themselves during the Last War, and like nothing better than drawing swords and riding out on horseback to defend it.
Dwarves: Dwarves live in various holds in the mountains, you will be surprised to hear. Their Mark of Warding lets them run guilds specializing in banking and defense, and naturally they also do extensive mining and smithing on the side.
Changelings: This crossbreed of doppelgangers and humans is now a true-breeding race in its own right, although it’s pretty similar to both parents. They’re generally found as rogues, unsurprisingly, though they’re as adaptable as humans. Their main shtick is to be able to do a Disguise Self thing at will. Changelings never have dragonmarks.
Kalashtar: This is a psionic race, but I think I’m going to skip psionics for this game, so these guys are out.
Shifters: Like changelings, shifters are a crossbreed, of lycanthropes and humans. They have the power to shift into a crossbreed form — maybe growing razor claws, or a tough hide, or being able to make huge leaps — a few times per day, with it getting more powerful as they spend more feats on it. They tend to be rangers or other wild/frontier things, and never have dragonmarks.
Warforged: These guys are the weirdest of the new races, and are basically like living, intelligent golems. They don’t need to eat or sleep or breathe (although they still have to rest before memorizing spells). Curing spells only have a partial effect on them, and there’s a different set of repair spells that work instead. The oldest warforged is only like 15 years old, as they were all built during the Last War to serve as troops, using special magical creation forges (although interestingly, there are some signs that warforged-like artifacts have been found on the southern continent — could the creation forges have been secretly developed with magic found there?). Discrimination against warforged is still pretty widespread: although the treaty ending the Last War gave them full citizenship rights in all the signatory countries, that doesn’t mean the average person doesn’t still think they’re hella creepy.