Thread Necromancy. I stumbled across this accidentally while Googling something else, and figured, hey, what the heck. This discussion is always interesting, if I can jumpstart it.
In many ways, I consider my homebrewing style to be more closely related to kitbashing rather than scratchbuilding. While I do have, probably, at least a few reasonably innovative ideas, I'm much more likely to just combine stuff that I already like, modify it just a bit so the borrowing isn't too immediately obvious, and run with that.
So, first off, my racial line-up is highly modified from the D&D standard. No dwarves, elves, halflings or gnomes or orcs or goblinoids or any of that jazz. Although largely humanistic, I've got wildmen (started as shifters from Eberron, although they started migrating a bit more towards tharn from Iron Kingdoms over time with simplified rules), jann (same as azhar from Freeport, which are in turn, the same as fire genasi in conceptualization), and renamed and redescribed tieflings, including a true-breeding population of them that look kinda like Graz'zt or maybe a unicolored Darth Maul. Stole the notion of Bael Turath from the "points of light" 4e setting, renamed a bit to Baal Hamazi. Also; I have Neanderthals from Frostburn--just for fun.
I stole the notion of a kingdom of vampires from an article I read on the Wizards website in support of the release of Open Grave, although I mostly developed the details of that myself after brainstorming with some folks online first. Since I stole (and renamed and reskinned) the azhar from Freeport, I figured why not go all out and modify Kizmir into my own Qizmir--a young, vigorous nation ruled by jann who are overlords to a subjugated population of humans. They're kinda on the perifphery of my setting, although colonists, traders and especially Barbary pirates who ultimately hail from Qizmir play and important part of my setting, and the Barbary Coast is a semi-independent group of cities founded by the Qizmiri. I also made a nation of hobgoblins that bears a strong resemblance to the skorne of Iron Kingdoms--although I've since done away with goblinoids and made them just a separate ethnicity and nation of humans since first formulating my setting. The resemblance isn't as strong as it was when I first "stole" it from Monsternomicon 2, but it's also not completely gone. And my "main" kingdom in the area is actually stolen from history, mostly, not a published setting. I concieved of it as similar to the Crown of Aragon at it's height.
Although I do admit that I like the "look" of Cygnar for these guys--again, borrowed from the Iron Kingdoms.
The behind the scenes movers and shakers villains of the setting are heavily influenced by the Ten Who Were Taken from The Black Company. There's a lot of Lovecraftian influence, although I'm not sure that including Lovecraftian elements in RPGs isn't more of an in-joke these days than anything else. I had my poorly defined Cannibal Isle culture gradually start to take on attributes of the Witches of Dathomir after watching those episodes about them on The Clone Wars with my kids.
Like I said; a kitbash approach. My setting includes more elements that started out as a "stolen" element and gradually evolved into something more or less unique than it did elements that were genuinely unique to begin with.