Neat, how did you make this? its pretty cool
The Steam Grid icons are 460x215, and so that's unofficially become a standard for game icons. Just go into Google Image Search, set the Size filter to exactly 460x215 and search for games you like. Then in Photoshop or whatever editor you use, paste the images into a large blank document and get them lined up with however you like.
Some games, like Daxter (PSP) and Heavy Rain (PS3) don't have them, so you should try to find either a larger image and scale it down, or get an image of the game's logo and resize it to fit within a blank 460x215 square and then add a background colour (maybe add a character if you want to be fancy).
