The Corporates
"You wanna solve all your problems, berk? Find out whose getting all the cash and kill them."
-Common Sigilian advice
The Corporations are among the most ambivalent forces in the Planes. On one hand, they've helped the Planes chug into the future. The Corporates petty struggles and competitions have generated vast amounts of technology and development, even the Planes of Chaos have seen some benefit, even if it's because they stole the tech off some military installation. And yet, they've also caused a lot of trouble and conflict, the average Joe Planar still puts their problems directly at the Corporate's feet. And, half the time, it will be their fault.
Y'see, the Corporates have an awful lot of power. The Planar Trade Consortium, once one of the biggest commercial powers has now retired to the backseat and become a lobbying group for the Corporates, encouraging Sigil, the Primes, and planar nation-states to loosen their grips on the economy and leave it to the good ol' sisters Supply and Demand. Most planar states, however, cast a suspicious eye at the Corporates, because there's all sorts of bad blood.
The Planar Trade Consortium (the PTC) used to be huge. They had figured that this black substance, called "oil", would one day make them rich, so they spent a lot of money buying up all the sites where they could get it, even if they had to build a fortress in the Abyss (which they did, ever heard of the 661st layer of the Abyss, the Black Ocean?). Originally, oil was used to light street lamps, but when some wise cutter found out they could build generators and cars and plastic, well, oil began to see really, really high prices.
The Planar Trade Consortium had an extremely tight hold on the oil market. Whenever a new oil well was discovered, the PTC would find some way to take it over through purchase or subterfuge. Eventually, The Authority (more on that later) ordered the PTC to split up or the PTC would be forcibly split. Estavan told the Authority to stick it up their ass, and The Authority never directly responded back. Instead the PTC suffered massive internal corruption (most say encouraged by The Authority), and like an old man with clogged arteries the PTC as a corporation bit the bucket, it's prior holdings sold off to the highest bidder.
Another score for the Corps was the Astral War. Y'see, the Astral War what established some of the most powerful and oldest corporations, like the current top-dog Valor Inc. In the rush to get weapons both sides bought as much as they could, not really caring who was selling what to whom. Now, some companies stuck with one side, others giving to whomever had the money, and some damn-right excited at the prospect of war. The Corps have been known to instigate wars so that they could get more customers.
Planars recognize five different "blocs" of corporations with similar histories or traits. These blocs are listed here, in order from strongest to weakest.
The Astral War Bloc
These corporations are among the oldest and most powerful, they were crucial in the arms race in the Astral War, some aligned with one side (such as Ortho Industries and Astral Manufacturing Inc.) or dealt with both sides (such as Valor Inc.). There aren't many, but they're all pretty powerful and established. From strongest to weakest, Valor Inc., Orthos Industries, Solaris Pharmaceuticals, Astral Manufacturing Inc., Mechanus Research and Technology Company, Goldcounter Industries, and Gunniver & Sons.
The ex-PTC Bloc
These are the organizations which used to make up the PTC until they split off, including the old PTC itself. There used to be hundreds, but out of that only about two dozen still exist today. Most of them are still pretty powerful. From biggest to smallest Black Ocean Oil Co, Acheron Refineries Inc., IPTC (Inter-Planar Transport Company), Hurcule Robotics & Plastics, the PTC and many more.
The Faction Bloc
These organizations are companies which are strongly aligned with or owned by certain factions. Hardhead Inc. (actually a conglomeration), companies owned by the Fated, Doomguard military research, and many others are part of the Faction bloc.
The Net Bloc
These are the "newcomers", so to speak, and the ones that profit the most from cyberspace. There are constant newcomers, and most die before making a profit. However, some have made millions and have enough money to threaten even the Astral War bloc. These include, from strongest to weakest, Marketplace.com, Bytopia.com, and ManEatsDog.org, as well as thousands more. Not quite as rich but not really mentioned much are the "adult" bloc, the most powerful is Tiefling.com.
The Prime Bloc
These companies originated on prime worlds, also called the "clueless" bloc. While they haven't got much of a foothold on the planes they're hard to get rid of, especially since they almost completely dominate their native worlds. The Prime Bloc is dangerous but small, but there are many hundreds. They've got their own lobbying organization, the Prime World Advocacy Group, and have been instrumental in getting planars to pay some more attention and respect to the Primes. Haverstadt Textiles is counted the most powerful prime corporation (and the most infamous), followed by Carter Ore and Minerals, Puretina Water, and many, many more.
The Belief Bloc
These three companies make up the weakest bloc and the strangest. These corporations actually were spawned by pure belief, they were never founded, they are purely based on people's perceptions of corporations. In effect, they are caricatures of real-world corporations, and something of a joke among planars. They also have a tendency to act bigger than they actually are. They include Celestia Productions, Baker and Thompson Finances, and Darkness Inc (yes, that is the real name).
The "Other" Bloc
There are those companies that don't fit into any of the major blocs, the ones which predate the Astral War yet didn't profit, or whose operations are so esoteric or illegal there's no point, or they're just too small to be corporations, and any number of reasons.
More to come...
I'll point out that the Catholic Church is the world's oldest corporation (followed by some universities, if memory serves).