Valve
Bethesda
Bungie
Ubisoft
Lionhead
Simply because they make my favourite games. L4D and Half Life, plus obviously Portal and Team Fortress 2. Bethesda are responsible for the epic greatness of Oblivion and Fallout 3, Bungie do Halo which is my all-time favourite modern game. Ubisoft are just generally awesome, but especially for Assassin's Creed. And Lionhead are run by the great Peter Molyneux, and I guess Fable 1 and 2 aren't really that bad when you get right down to it. Plus I'm actually looking forward to the release of Natal and Milo, and finally Lionhead are British, so I'll probably be applying to them for a job in five years time...