Classy icons crafted according to Microsoft guidelines. Available in PNG and SVG. Free for a link
Jet Admin - Build business apps really fast
Feather Icons - Simply beautiful open source icons
Retool - Build custom internal tools in minutes.
IconStore - Free icon packs by first-class designers
Blur Admin - Angular admin panel front-end framework
Flat Icons - 20,000 unique, customizable icons with free lifetime updates