I saw these pop up on Twitter a few weeks back, but you know what? I've been on holidays for a few weeks. So here they are. ***** Artists is a page on Steam's community hub that showcases the work of Valve's art team, past and present.
There are rough sketches, promo pieces, 3D renders and joke posters, for just about every Valve game under the sun, from Alien Swarm to DOTA 2 through Left 4 Dead, Portal and Half-Life.
***** Artists [Steam]