I'm sure lots of folks will tell you Kalamar, and that's probably a pretty good recommendation, although I'm still trying to plow my way through the campaign book. It's good stuff but the writing is dry so you have to make an effort to get into it.
If you have access, I would recommend Birthright. It's second edition and the rules focus on ruling your own domains (kingdoms, churches, guilds, etc.) but if you're just looking for a campaign world, you can ignore all those extra rules and just use the setting materials. It's an excellent world, low magic, gritty and realistic, and handles the interaction between different cultures very well. There are five major human cultures, each of which is broken up into lots of smaller nations. The demi-human cultures stand apart from the humans more so than in other worlds and there is often lots of friction between the races (especially between elves and humans).