Looking at the games I've owned and played most in the past few years...
Valve - HL1 (well only the mods were the reason I played so much) and HL2 were released stable and kickass games all-around. Great support from Valve for mod makers like easy access with Steam (which I find awesome) and developer resources. I remember right after buying HL1 on release, I had some sort of CD key problem, so I emailed them. I still recall to this day that it was Gabe Newell who replied back as tech support and helped me solve it!! Will more than likely buy Ep2/TF2 right away and no matter what.
NCSoft - I bought Guild Wars original back in 2005 and even at release it was very stable, graphics and performance good, and overall felt polished. They have not abandoned it either, as seen by the updates and content/festivities that go on to this day. My old roommate bought Nightfall and it too seemed extremely polished. From what I've played with the Tabula Rasa beta, I could probably now say NCsoft has a good enough track record for me to trust on day one.
I guess that's about it. But for somewhat consistent and good devs to me:
iD... really liked them for Q1 and Q2, somewhat Q3, but not much other releases.
Codemasters... pretty good mostly because they are one of the few that release racing games on the PC still, and quite a few have been good.
Epic... I haven't played many Epic games that I recall. UT and UT2k4 were awesome and polished, but I don't recall any other games from them!

Looking forward to GoW though.
I would say Blizzard... but outside of Diablo and moreso Diablo 2, I just never got into their games like Warcraft and Starcraft. Was always a C&C fan instead.
Relic, Remedy, Firaxis... don't have a lot of games from all these guys, but the few I know they made have been very very good, so they are quite trusthworthy.