And still no mention of Yoyodyne in Thomas Pynchon’s novels. Well, somebody had to do it.
[url=http://boards.straightdope.com/sdmb/showpost.php?p=7319986&postcount=11]
Missed it by that much…
Without preview and without googling, WHIZ was were a certain Billy Batson worked, and APEX… wasn’t.
I don’t know APEX, 
OK, you got W.H.I.Z. Radio.
Anybody wanna try for Apex Broadcasting? Hint–Gotham City.
Oh, I’d forgotten ConHugeCo! (In many of my conversations, every large corporation mentioned becomes 'A wholy owned subsidiary of ConHugeCo. I think the original reference is from an MST3K, but I could be wrong). CHC, please. 
I am Presteign of Presteign, and I do not know my stock ticker symbol; I have people who know these things for me.
And speaking of Bester, there’s also Monarch Enterprises and the D’Courtney cartel.
References are from Alfred Bester’s The Stars My Destination and The Demolished Man respectively.
From Babylon 5, there is Interplanetary Expeditions (IPX), the rather unscrupelous Terran corporation which has a habit of unleashing various ancient alien mishaps on humanity (with such classics as the Icaran Superweapon, the Shadow Battlecrab on Ganymede, and the Vorlon Thirdspace Gate to their credit).
From the Vatta’s War series by Elizabeth Moon, There is also Vatta Transport, and its parent company (Which I belive is the Vatta Trade Syndicate, VTTA perhaps?), along with InterStellar Communications (ISC) and the Mackenzie Military Assistance Corporation (MMAC)
And, while you’re at it:
Horizon [HRZN]
NeoNET [NNET]
Evo [EVO]
Cross Applied Technologies [CAT] (or [RIP] for SR4 fans… :D)
Mitsuhama [MITS]
Wuxing [WUXG]
Neuromancer’s Tessier Ashpool was a private company, like the real life Mars chocolate people. Not listed, so it wouldn’t have a stock exchange code.
Similarly, the massive Planetary Organisation is almost certainly private, owned entirely by one man, Elijah Snow.
Kord Corporation (under administration, no doubt, following Ted Kord’s death) from DC Comics (KORD).
Hmm. Also the bad oil guys in the current Vertigo Comics series The Losers.
Apex Broadcasting was the radio network the Golden Age Green Lantern worked for in his secret identity of Alan Scott. Post-Crisis, GAGL was Gotham City’s defender, pre-Batman.
Just remembered one from a favorite old series, the Chartered Zarathustra Corporation from H. Beam Piper’s Fuzzy novels. Don’t know if there was ever a ticker acronym given. Probably CZAC.
Muppet Labs (MPTL), Where the future is being made today!
IIRC, the only corporation mentioned by name in all of Star Trek’s various incarnations was the Dytallix Mining Company (TNG “Conspiracy”). Its ticker name, I presume, would be DMC.
Not sci-fi related, but am I the only one who remembers Bob? Bob tells his family that his comic has been picked up by the American-Canadian Transconitinental Communications Company.
Trisha: “You mean AmCanTransConCommCo?”
Not sci-fi, but from The Simpsons (exact corporate names somewhat speculative):
Burns Nuclear Power Co. (BNP)
Mr. Plow Inc. (MPI)
Duff Breweries Corp. (DBC)
The Leftorium Inc. (TLI)
Krusty Entertainment Ltd. (KEL)
Lionel Hutz LLP (LHL)
Canyonero Motors Corp. (CMC)
The Android’s Dungeon Enterprises (ADE)
[geek] Actually, on Shin-Ra’s logo, it’s spelled out as
Shin-Ra
ElectricPower
Company
With the letters SEC bolded. Therefore, I’d say SEC. [/geek]
Although the Securities and Exchange Comission wouldn’t be happy about it.