Here’s a handy resource that I will be sure to use in the future: game-icons.net.

The site has thousands of icons available under a CC by 3.0 license. I am not a lawyer, but by my read this means you can reuse, redistribute, and remix the icons provided you give appropriate credit, indicate if changes were made, and provide a link to the license.

Check the site out and tweet me if you use or have used the icons in your game.