Tolkien and Lloyd Alexander, and a bunch of unrelated authors that gave me inspiration for nations/politics/etc.
You see, my campaign world can be broken down like this...
Names, Places, etc.: 50% Tolkien, 20% Lloyd Alexander, 30% 'unique' (or 'too many sources to quantify')
Backstory, History, etc.: 75% Tolkien, 25% Unique (basically, I took the 'structure' of Middle Earth's history, and filled in my own sorts of details, bent things around, and made it my own, while still having the Middle Earth feel that I was going for.)
'Literary' Themes (good vs. evil, the conundrum of free will vs. fate, and so on): 25% Tolkien, 75% Conglomeration of everything else I think is good.
The Way Things Work: 90% unique, based on real-world politics, demographics, and so on, 10% Tolkien.