Atlas Icons
Over 2000 free icons available in mutliple formats, including webfont and SVG. You can adjust the size, color, and stroke thickness before downloading. These are under an MIT open source license.
illustrio: 100% free, 100% customizable icon library
Free icons. You can easily get the same icons in different styles, and you can pick your own two colors.
60 Free Outline Icon Sets Perfect for Contemporary Designs – Design School
Free icon sets. Some of these are very specific (Christmas and New Years), but several large sets are included that would work for elearning
Flat Icons & Icon Fonts | CSS-Tricks
Large list of icon fonts, many of which are free