Many proprietary fonts are encumbered by copyright restrictions, so I always keep an eye open for sources of free fonts. Even so, just because someone announces a font is free on a website, if you plan to use a font in anything you publish, it is wise to first check the font license. I will continue adding to this list as I discover new font resources.
And of course, I welcome any additions you share with me
DaFont is where I found the beautiful public domain “Rebel Caps” font I selected for the title type face of
SIL International developed the OFL (Open Font License) and provides several excellent fonts, including Gentium and Charis.
The Fell Types offers an interesting historic view
and of course there is Google Fonts, which are designed to make it possible to use free fonts on websites. I myself have a problem trusting any corporate entity to continue supporting any software forever, so I prefer to download any fonts I use there. Google discourages such font downloading, since it makes it more difficult for Google to track the use we make of such fonts.