Like if you take Belgium for example;
- Steve Jackson games produces GURPS Belgium, which gives you more detail about Belgian history, culture, and personalities than you ever needed, with a small section of creatures from Belgian folklore in the back.
- Palladium produces Rifts Mystic Belgium, which gives you rules for alien squid that focus on bio-engineering, AI controlled jetbikes, the Belgian Knight OCC, and rules for pommes frites.
- White Wolf used to produce Brussels by Night, which was a pretty good supplement if you could ignore the way the index didn't actually refer to the book and the historical note about Richard I resisting a siege in the great Belgian castle of Chateau Gaillard.
- WotC is planning to release Heros of Belgium in October '06. It'll include rules for Belgian dragons, how to work Belgium into your existing campaign, 15 Belgian prestige classes and 18 new Belgian feats. What I've heard is that you can build a real juggernaut if you give a dwarf Barbarian the Walloon Champion prestige class, Weapon Finesse, and Spiked Chain.