Classy icons crafted according to Microsoft guidelines. Available in PNG and SVG. Free for a link
Feather Icons - Simply beautiful open source icons
Merry Christmas Design Assets - Over 40,000 high-quality Christmas assets from Iconscout to bring the spirit of Christmas to your designs.
IconStore - Free icon packs by first-class designers
Creative Market - Buy and sell handcrafted, mousemade design content like vector patterns, icons, photoshop brushes, fonts and more at Creative Market.
Flat Icons - 20,000 unique, customizable icons with free lifetime updates
Christmas HQ - Totally free holiday icons, images, borders and fonts