Reading this line I should recommend you the Kalamar setting, you have 6 human races in the world and each one is really different from the others, plus you have the Hobgoblins as a civilized race. There's some other races cities or towns so you have a few Elves, Dwarves and the other common races from the PHB in the world.
If you buy the Campaign setting book, you'll get lots of adventure hooks and depth info of the world, there's like two 3E rules in that book, all the new rules that Kalamar uses are on the Player's Guide, inside that one you have some PrCs, Spells, Feats, the Sub-Races like Golden Halflngs and Half-Hobgoblins, there's some new Core Classes in the book and it's a really good book overall, some feats are on the power side but they're only a few.
Also you have Geanavue, a city book written by Ed Greenwood, it's a good recommendation if you want to run a political campaign but not too usefull if you have something with more action in mind.
There's the Orc book that details the Orcs of Tellene and the five sub-races that live in the world, some new equipment and feats for Orcs, advice on playing an Orc as a player and depth description of the Orc society and the major tribes of Orcs in the world. Really good one with good reviews in EN World.
The Hobgoblin book just came out and will be in stores next week, sounds like the Orcs book but for the Hobgoblins.
Of course there's the DM Shield that you should get no matter what campaign you play since it's the best 3E D&D screen I've seen, this is another one with really good reviews here.
You have a bunch of Adventures that "exapand" the world, most of them details a bit of the world a bit more and they come with the ImageQuest pictures, those are a set of drawings that come in the back of the adventures that you can show to your players of important places/people in the adventure.
If you like maps, then you must get the Atlas. It's an Atlas of the world but they do it like a real one not a fantasy Atlas, so you don't have strange things in the maps. Some people complain about the "blue pages" on the Atlas but the guys at Kenzer put those because some people want to buy two copies and tear them and made one huge wallpaper of the world, they already do that in the Kenzer office from what I read on the message forums.
Besides all those books that you can already buy, you have in the future a Monster Book for Kalamar in June, a book about the Pirates of the world (think this one comes with a set of rules for naval combat), a book of the secret societies of the world that's in the work right now and a book about the religions of Kalamar (Don't forget you have 40 Gods in Kalamar), almost forget there's a book on the Secrets of the Alubelok Coast that details one area of the world.
Well hope this helps you to define your choice, I DMed on Kalamar and my players have all great time, I never try Scarred Lands yet but seems one of my players want to run a campaign there in the future.
Cya, Cazador.
