Professional Game Usability

Here are a few companies that do games usability:

UK:
Epicentre (Brighton) are a part of Epic, and say they do games work too.
AmberLight (London) are a usability company that have done some games work before, particularly with Sony.
BunnyFoot (Oxford, Edinburgh, London) do games testing and have written some academic papers too.

Europe:
Experience Park (Hamburg) do the regular usability stuff with games

SQA Partners (Estonia) also claim to conduct games testing, and refer to Sony's TRC and Microsoft's TCR. However their test lab does not appear to be set up for console usability testing in a home-like environment.

Australia:
Usability One (Sydney) are a usability company that seem to do all the regular stuff with games

USA:
Orbus Gameworks (Boston, MA) "Aleph Metrics Suite" does data collection - but how do you analyse this data?

Valve (Washington) track some data in SteamWorks, their electronic distribution / community solution

Behavioristics (California) is Desurvire's company (with published games usability papers) where they use RITE and more typical usability methods, they also mention "Game Metrics (new!)" but have no details about what this means to them.

Xeo Design (California) are run by Nicole Lazzaro, who's written pieces on user testing and emotions (also in the HCI Handbook, in the same chapter as Pagulayan et al's)

And of course there's Microsoft (Redmond)

Ronin UX is Bill Fulton's (ex-MGSUR) company. They look like they do general usability, but Fulton's publications include loads of important games usability (thanks Darius!)