Well, Dwarves seem like solid earth benders, while Elves would probably be straight water benders with a preferance for the plant-manipulation "subclass". Air benders....Gnomes or Halflings would be great, small size and nimbleness and all that jazz. Orcs and Goblins are also prime fire benders. Lets say, for convinance, each race has two distinct affinites, and have there own "mastery" ability that lets them do a trick typicly found only among there benders (as a guideline, not sure if your system can do everything on the show. Worth a shot, however.)
Dwarves are known firebenders and earthbenders, with metalbending being known among there most powerful.
Elves are airbenders, waterbenders, and
earthbenders, and are known plant-manipulaters. To be exact, high elves are airbenders, "woodsy" elves are actualy waterbenders, and the wild elves are earthbenders.
Halflings are known to be both waterbenders and earthbenders. If your letting Ebberan influence you, the Talanta are the local sandbenders.
Gnomes are airbenders and firebenders, and they are well known for mastering the ever lovely lightning-creation trick. So yeah, Ozia? A gnome.
Orcs are potent waterbenders and firebenders, and there greatest fighters can do a Combustian-Man like explosion of fire. Goblinoids have the same affinites, but instead have the ability of healing passed down from generation to generation.
Drow who live on the surface tend to be waterbenders and are known for there cruel Bloodbending, firebenders exist in small amounts in small island cults, and earthbenders exist in there underground cities and can often make a small fortune off there talents.
Giants would just have whatever is most fitting, realy. Might be fun to have only one giant race, and have each "race" of giant simply be a base for a Bending specimen. Hence, every fire giant would have levels in firebending, every cloud giant would be potent airbenders, ect. They might be a base for humanoid spirits.
Building on the idea in my last post, Genies were the original benders. Marid's taught the art of waterbending, Dou occasinaly went out and took on creatures who lived near there domaines as charges, ect. Most likely, the average Genie the party would come across would have more than a few levels in the sutable class if this is used. As a twist, Janni have the ability to take levels in more than one bending class, befiting there mixed nature.
And finaly, humans have the chance to have any of the bending skills, but have a far smaller chance at learning any "nitch" skills.