The fundamental duality of things is found in so many belief systems it would be hard to list them all. It's by no means a patently Taoist concept.
A few obscure examples, briefly:
Qabalah: (another word with no "official" english spelling)
Jewish mysticism. The "tree of life" diagram used in Qabalah charts the path from nothingness (the realm of the Absolute, also the level of divinity) to somethingness (the realm of the Relative, the level of matter). Something cannot "exist" unless there also exist things that are not that thing. The material world is defined by exclusion... to name something is to differentiate it from everything it is not. The "God" of many belief systems like this one "exists" at the level of the absolute, because it's absurd to imply there are things that the all-encompassing does not encompass (this also puts the entity above locality, time, and consciousness as we understand it). The two sides of the diagram counterbalance each other. One side injects boundless, shapeless energy. The other imposes rigid, structured form (basically disciplining that energy into the capacity for a relative existence). As a creation zig-zags its way down the diagram, it gains complexity and organization until it reaches the material plane.
Hermeticism:
Associated with alchemy. Rooted in ancient Egyptian belief systems (as Christianity is in many ways). Has so much in common with Taoism as far as duality that there's debate over whether one influenced the other somehow. In Hermeticism it's more accurate to call it "polarity" though, because rather than having two binary states, there is an infinite gradient between two extremes (I doubt Taoists disagree with this). Hermeticism also sees the cosmos as a fractal. It's hard to describe, but if you've ever seen a fractal diagram, you know that as you zoom in or out the pattern remains identical. So not only are there these polar extremes, but there are "octaves" of transcendence one traverses on the path to divinity... the different planes echo each other and affect each other, and are each polar as the one above and below are.
Huna:
Hawaiian shamanism. Given a lot of attention because it's considered to be one of the least corrupted ancient belief systems on the planet because it took religious missionaries so long to find out the Polynesian islands even existed. There has still been influence obviously, so people are still unsure of what's truly authentic. Huna has "octaves" as well, in a way. It describes a framework for generating creations on our plane (somewhat like the previous two belief systems) through recognition of the dual nature that things have. You bring something down from the realm above this one by polarizing it into itself and its opposite (on the plane above, it was unified). You lift something up to a higher realm (including yourself) by depolarizing it or unifying it. Presumably the unified entities on higher realms have their own opposites which are reconciled on the next level up, and so on (you could visualize it as an upside-down branching tree). Part of the shaman's power comes from the awareness that something and its opposite are the same thing... the illusion of duality is merely a problem of perspective.
The list goes on and on. It can be amazing how philosophers of various cultures can come to the same conclusions about things. You'll even find some of these themes in esoteric Christianity. In exoteric Christianity, err, well, not so much...
I know these descriptions are somewhat superficial and possibly incoherent... I was busy and had to type it quick. Just trying to give a taste of them. I wanted people to be aware that there are other philosophies out there beyond the ones society beats us over the head with.