Google Material Icons

Google developed a visual language that “synthesizes the classic principles of good design with the innovation and possibility of technology and science”, which they called “material design”. Google retains a living document of specifications of the material design. As part of the specifications, Google provides a library of system icons, created based on Google’s design principles, for download. Users can search or browse the icons arranged by categories.

Freepik

From vectors to PSD files, icons and stock photos, Freepik provides resources for graphic and web design. As of August 2015, the site has received more than 440 million downloads. Developed by “a team of designers, developers, professionals of marketing, communication and administration” based in Spain, Freepik offers two types of content: free and exclusive graphic resources by Freepik, and graphic resources belonging to others. Users can search or browse by categories.

IM Free Collections

Provided by web design agency, IM Creator Ltd., IM Free Collections is “a curated collection of free web design resources”. The images are from various image sources that provided these images on Creative Commons licenses. Users can search or browse by various categories.

Noun Project

Launched in 2010, The Noun Project is an online catalog of downloadable icons and symbols submitted by designers around the world. Users may search for png or editable svg files of the icons.