My "Hot" Patchwork Homebrew
My homebrew setting, Thraevin, borrows heavily from dozens of sources. I've found that if one borrows from enough dissimilar sources, one produces a unique mix that's not entirely recognizable at first glance.
To give you an example, my current Urban Campaign draws directly from the following:
Arcana Evolved: The backbone of my campaign, I use pretty much everything out of the book except for the Oathsworn class (I prefer Monk), the Dracha race, and Evolved levels (Not a fan of magical evolution or AE style Dragons). Some setting material, such as the Verrik Curse and the basic psychology of the races is retained, but a lot is altered to suit my needs.
Core Rules: I use the Barbarian, Monk, and Rogue classes from the PHB to supplement AE's classes, and frequently use monsters from the MM1. The DMG is an invaluable asset, since AE assumes that you have one as well (it's just a replacement PHB, afterall).
Complete Adventurer: I use the Scout base class, many of the PrCs, feats, and equipment. (Alchemical capsules have almost become standard assumed PC equipment for my games).
Player's Handbook II: The Sewer Worker's Guild (a sample affiliation) has been a major contact for the PCS, and I would let a character play the Knight class if they asked nicely. Feats and spells might eventually make their way into the system.
The Complete Book of Eldritch Might: The variant Bard sees quite a bit of use IMC, and I was able to include The Nexus and the Pool of Glenmasis ever-so-briefly thanks to the PCs helping a magic-shop owner "relocate" off-plane when the Inquisition came to town.
Oriental Adventures/L5R/Rokugan: One of the most common PC-able races IMC are the Nezumi, who I have a homebrewed set of stats for that includes 3 racial levels in the AE style (I use them instead of Dracha as the +2 Con, -2 Cha race).
Sorcery & Steam (by Fantasy Flight): The PCs are working for Dr. Samius Freeman and frequently visit the Freeman Clinic for medical attention. They rely upon the Orphan League to gather information about the city and their foes, and have run afoul of Roderick and the Marauders. All the flintlock and matchlock firearms from this book are available IMC.
Cityworks (also by Fantasy Flight): We briefly had a PC Acrobat, and I've used Pit Fighters as opponents.
I've also drawn monsters from a wide variety of sources. The PCs have an Albadian battle dog (Creature Collection 1) as a pet, and have fought char fiends and rumblers from the same book. The first storyarch of the campaign involved fighting off a fungal infestation of the sewers which included ascomids and vegepygmies from classic D&D, resurrected to 3.5 by the Tome of Horrors. One of the major NPCs of the game is an inscriber from Denizens of Avadnu. Much to the consternation of my party, they also stumbled upon a factory producing mechanical dire badgers, dire bats, and howlers which used the clockwork creature template from Green Ronin's Advanced Bestiary. The Players don't know it yet, but the BBEG's lieutenants are creatures out of the Monster Manual II in humanoid disguise.
Lastly, my campaign's cosmology is essentially a combination of WarCraft and a discarded "crystalline spheres" model of the solar system made by Johannes Kepler (with allowances made for AE's Green/Dark dichotomy, the Akashic Memory, Totem Spirits, and the dead god-king Xyphon). The sun and the planets are all set into crystalline spheres, which in turn float in a negative-energy filled void called the Twisting Nether (which is a combination of Hell and the Astral Plane, really). The only other plane is The Emerald Dream, which serves as a sort of Platonic-Ideal blueprint for creation (and combines elements of Arborea and the Etheral Plane). Also like WarCraft, the known universe was crafted by a race of Titans, who made the Giants (AE) and Dwarves (modified PHB) to finish their creation, and empowered 5 powerful Aspect Dragons to watch over it all when they left. Likewise, daemons from the Twisting Nether are constantly scheming to destroy Creation.
At one point, I went through a phase where I thought that I might try and remove all the borrowed/stolen ideas from my homebrew, but then I read China Mieville's Bas-Lag novels, The Chronicles of Thomas Covenant, and Ptolus: The City by the Spire, and now I have even more influences to incorporate into the mix. By now, it's obvious that so much of the setting is borrowed that there's no point in trying to pull out everyone else's intellectual property, since that would leave me with very little to work with.
I might try my hand at publishing a setting one day, but I'm afraid that right now most of my intellectual energies are tied up in this wonderful messed-up mix of borrowed ideas. In any case, 17 happy players across four campaigns and four years seems to indicate that originality isn't necessary for an enjoyable game.
Robert "And That's Not Even Counting Non-Fantasy References" Ranting