Web developers can get free icons for their project using below resources.
Fontawesome - Font Awesome gives you scalable vector icons that can instantly be customized — size, color, drop shadow, and anything that can be done with the power of CSS.
Iconmonstr - It gives to discover more simple icons to your projects.
Icons8 - Here you can pick icons for apps with various colors, sizes etc.
Iconfinder - It provides lovely icons to much of designers.
Fontello - It is used to build custom fonts with icons.
Happy designing. Thank you.