素材が大量にある
http://icons.mysitemyway.com/legacy-icon-tags/3d/
その他
https://www.iconfinder.com/free_icons
http://www.iconeden.com/icon/bright-free-stock-iconset.html
http://icons.mysitemyway.com/legacy-icon/061301-blue-metallic-orb-icon-people-things-people-man11/
http://www.behance.net/gallery/FREE-flat-UI-kit/7747833
http://icons.mysitemyway.com/legacy-icon/018231-blue-white-pearl-icon-symbols-shapes-power-button/
リンク集のリンク集
http://kachibito.net/web-design/free-icon-seto-for-commercial-use.html