Man, if you'd started this thread in a couple of days' time I'd have had a much better post for you, but here goes. I know you were asking more about game artists than renders, but this might help anyone simply interested in having games on their wall (or desk). I've been gradually refocusing my site (deadendthrills.com) towards this for some time now: breaking the barrier between screenshots and print, which let me tell you is not a simple task.
You can get concept art and specially rendered art prints from various stores, or you can make what Crytek calls 'poster shots' by tiling in certain engines. I'm working on a book, though, which needs a much wider range of games shot at
photographic quality. Tiledshots and such can't include a lot of the screen space effects that really gel scenes in Mass Effect and the like together. As a strictly non-profit/charity venture, I'm also considering canvases, prints, etc.
Here's the real hurdle, though: pixel resolution versus print resolution. It's a problem publishers run into constantly because print favours (demands) something in the region of 300dpi quality to produce anything like the sharpness and detail you see on screen. Screenshots are almost invariably the equivalent of 72dpi, and even a 1080p shot will get you little more than a postcard. So, I've tweaked my monitor driver to think its native resolution is 2160p (3840x2160) and now run my games at that resolution with moderate antialiasing. And I've run some tests with a local photographer whose clients include Aston Martin, the MOD... I've no idea what use that information is.
Anyway, the size I'm planning for the book is A4 dimensions for the shots with a slight margin, and the quality level has to be perfect. They have to look better as a collection than anything seen in print before, and at risk of sounding completely arrogant they're pretty damn close. These aren't tiledshots, either, but simple Fraps grabs brightened in Photoshop. The next test will be to see how much dpi I can sacrifice as the size increases, and how that compares to the average poster which tends to have a low dpi anyway. Tiledshots can, of course, be rendered at whatever pixel resolution you want. There's also the question of materials, and it'll be interesting to see how the 2160p Okami canvases come out.
Like I said, though, I'm right in the middle of sorting that stuff out so this is a little premature, but it seemed relevant enough to post. While the print stuff's going on in background, my site's going to be hosting daily image updates with download options for 1080p (which will be downsampled from 2160p for perfect IQ and geared for wallpapers) and the original 2160p (or in some cases higher) in case you want to try making your own prints. If you do, though, I can't stress enough the importance of paper and printer. Take them down to your local print shop and ask for the satin photographic paper or the equivalent; don't settle for 'gloss' or anything like that as it's the stuff they use in their photocopiers.
To give you an impression, these aren't exactly the stunning compositions I had in mind but they're what I've been testing with. Click the thumbnails (pretty big thumbnails, mind) for the 2160p versions:
