Dafont offers more than 13,000 Fonts. That’s a lot, but they’re categorized and offer previews of your custom text.
Font Squirrel offers a selection of fonts which are cleared for commercial use.
Lost Type has a small number of vintage style fonts. Not technically free, instead, it’s pay what you want.
The League of Movable Type aims to offer an elite selection of open source fonts.
Fontspace has more than 15,000 fonts.