UI Movement - The best UI design inspiration, daily
Call of Duty - Call of Duty is a first-person and third-person shooter series by Infinity Ward.
UI8 - Carefully crafted UI design assets
Quake - Quake is a series of first-person shooter video games released by id Software.
UI Garage - Specific mobile and web design patterns for your inspiration
Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.