the steam cover gallery
yeah so i made these with source filmmaker. feel free to download any of them to use in your own library, but they're gifs so you'll have to convert them to APNGs using a site like ezgif.. they may take a second to load.
if you're looking for non animated ones or just not satisfied with one of these (i'm guessing 3 or 4), here's a link to FlumpaBump (also known as Squimpus)'s really good ones.