Chaosium is well-known for putting out a quality product. The books of theirs that I have read are remarkably free of fluff and filler, instead concentrating on giving a gamemaster the ability to run a game "out of the box". This is a great attitude, and something I look for in companies I buy from. Chaosium games have their own feel, as well; they seem to be a bit more classical than many companies. The games are clean and have high production values.
Additionally, Chaosium maintains a strong net.presence, and their employees have always been friendly and helpful when I've spoken with them at Gen Con.
The writing and attention to detail in FASA products is also worth noting. One of the first Shadowrun supplements, The Seattle Sourcebook, has more than enough material within to provide a year's worth of weekly gaming sessions, and it presents that information in such a way that players can read it and not spoil the GM's plans.
1999 Update:
I don't have a lot to say about FGU, as they didn't make much of an impression with me before they folded; I bought V&V pretty young. Three-year-old rumor implies that FGU won't part with the V&V rights unless the buyer also purchases all of their backstock, a condition I would find horrifying.
It is hard to tell whether GDW was primarily a wargames company or a roleplaying games company. As far as I can tell they were a little bit of both. Surely a perusal of either T2K or T:TNE will tell you that the roleplaying games were written by engineers who wargame, but I don't know if that's all bad. Their rules systems tended to be very complete and internally consistent, if hard to pierce at first. I've heard other people say that their older RPGs were poorly playtested, most notably MegaTraveller, but I didn't buy much of GDW's product before about 1993.
Graphic design was overall okay before late '95; Vampire Fleets, for Traveller, was worse than some of the recent books they've put out (speaking graphically), but art quality had improved greatly in the last year and a half.
Sadly, GDW closed up its doors in January 1996. They had been sued in '94 or '95 by TSR, claming that GDW's Dangerous Journeys was written in part while its writer, Gary Gygax, was still a TSR employee. Between the DJ suit, the problems selling the hard-liners on Traveller's New Era, and slow sales in the industry as a whole, the company could not afford to go on, apparently. GDW was one of the oldest publishers in the industry.
1999 Update: Steve Jackson Games has bought a license to publish Traveller under the GURPS system, and brought Loren Wiseman, once of GDW, on board.
1999 Update: Quality control, finance control, and other sorts of control problems combined to shut IG down last year. Steve Jackson Games is currently the only company producing Traveller materials. Imperium Games Web Site
1999 Update: ICE has released a nifty new pirate game called Run Out The Guns! that's a heck of a lot of fun to play. I highly recommend it.
I can't figure out whether Last Unicorn is a collection of geniuses or instead self-important gits. Certainly LUG's recent releases have been ambitious and well-received. I hope they can keep that quality level up.
1999 Update: Last Unicorn picked up the lucrative Star Trek RPG license. The new ST:TNG:the RPG looks very pretty, is apparently well-written, and would probably be a lot of fun to play, if I had any free time.
I don't know much about Palladium; I don't spend a lot of time playing their games, and I have only bought one of their products. I can't say I'm very impressed with them in general, but it's for reasons I can't entirely articulate.
No, that's a lie. The reason that I'm not impressed with them is that they cater to early-teen munchkins, and they don't have good quality control on the books of theirs that I have seen.
I root for SJG. I like them. I continually hope they do well, and I've got an article or two I hope to get into their magazine, Pyramid. The recent influx of cash from Illuminati: New World Order has done good things for them; I hope they're able to keep it up. They make quality stuff, and despite the fact that I never run GURPS, I continue to buy GURPS sourcebooks, they're so good.
1999 Update: As most folks know by now, TSR is now owned by Wizards of the Coast, and has a much more progressive Net policy than it did a few years back. Their newest game is Alternity, which is intended to do for SF roleplaying what AD&D did for fantasy. We'll see, I guess.
West End seems to be a young company, relatively speaking. Their success level varies; Torg was initially huge, but has since sort of died.
1999 Update: WEG is filing for bankruptcy protection; it and the shoe import company that WEG Owner Scott Palter also owns lost a lot of money recently. They're trying to pull out of bankruptcy and start publishing new stuff. I wish them the best of luck.
White Wolf is so weird.
They have gone through a lot of changes in the last through years. In the early days there was a lot of brilliant, innovative stuff coming out of the place, including Vampire, Werewolf, and Ars Magica. As time passed and later products came out, the company's reputation lost some value; some products were shabbily produced or poorly thought-out. It became an expectation that WW would release a second edition of each game only a year after the first release. The first edition of Wraith was poorly edited -- though the second edition is one of my all-time favorite RPG rulebooks -- and the first edition of Changeling involved collectible game components, a bad idea that must have looked like a good idea to someone at one point.
Lately, though, the publisher has improved in terms of dedication to its public, accessibility and attitude. Many gamers used to criticize WW's 'hipper than thou' attitude (IHNJH, IJLS 'Hey, Net Punks'); that's been toned down a lot. And they're putting out some very good stuff. Okay, disclosure time: I'm freelancing for them, so I'm prejudiced. But I had nothing to do with Corax or Kindred of the East or Charnel Houses of Europe: The Shoah (a controversy all its own, I might add, but a fabulous piece of work), and these have all received critical acclaim lately. And Trinity, the project I've been working on, is very cool. You should buy it.