Open Foundry
Open Foundry is a free platform for curated open-source typefaces.
1001 Fonts
1001 Fonts is an impressive repository of both free and paid fonts for use in design.
Font Squirrel
Font Squirrel is a "free font utopia" with many free fonts for commercial use.
Introduction to Typography
Fonts for Posters
dafont
dafont.com is another online warehouse of fonts. Lots to choose from, easy to navigate.
Fontpair
Fontpair has a huge selection of free fonts, pairings, and inspiration.
MyFonts
MyFonts is one of the largest font marketplaces in the world, with many free offerings.