I'd say the financial industry is a perfect example. There's a nifty result that maintaining market efficiency is an NP-complete problem, and the standard assumption is that markets are solving this continuously and more or less autonomously in a way that don't depend on any particular actor.

Krugman's model of currency crises for instance ends up with "markets" as a kind of Cthulu-esque omnipotent, amoral, and inscrutable actor.