Sadly, despite Fappy's good intentions, the more I think about it, the more I notice the devs that I w o u l d have followed... So many of them on top of countless memories... Shame *tear*. But:
Valve. Valve is the company that has not, to this day, disappointed me. I started playing the original, no mods, no expansions, garden-variety classic Half Life when I was 6. Then the expansions, then Counter-Strike and the first TF. I grew up with Valve and when I was all grown up they gave me Steam to spend my cash and Portal to remind me that I am, in fact, still a kid somewhere in there. Say that planets collide, cosmic events of titanic proportions unfold and Half Life 3 doesn't come out... ever, I'd still follow Valve into hell!
Bethesda. For being flawed and recognizing that, making the later-to-be ground shattering decision to release the G.E.C.K and stand behind a modding community firmly. Good on you, Beth!
THQ/Relic. Being a Warhammer 40K fan I want to see them rise and succeed. The strategy games were great and Space Marine has so much potential it really breaks my heart. I still play SM at that tiny, hardcore competitive stage and the people from the few clans that are left have one thing in common - those long, drawn out conversations about how the game could have been great and actually provided a massive multiplayer audience with hundreds of hours of epicness and fun.
Lastly, BioWare. Yeah, I'd still follow them. I want to see them either rise from the depths of the consumer eye to which they've sunk or watch them burn with a sadness in my eyes... Either way, I still hold that tiny hope that all those awesome moments they provided in the past count for something and are worth the loyalty.