Several public lists of "free" fonts exist. They all have their pros and cons.
Open Font Library
The Open Font Library is a young project dedicated to the creation of free/libre-open fonts. Any currently unpackaged font listed there is probably fair game for packaging (but do check our legal page anyway). In addition new external free/libre-open font references are regularly posted on the Open Font Library mailing list.
Fonts listed there are have been screened for legal suitability, but not for artistic quality or internationalization.
SIL has demonstrated strong support for free/open fonts, drafting our preferred license, and releasing many quality fonts.
We should probably package every single OFL-ed SIL font on this page. New fonts may appear there every once in a while.
Fonts listed there are have been screened for artistic quality and internationalization, but their legal suitability varies. Also only Unicode fonts will work in Fedora.
Unifont lists fonts critical for good internationalization. Most of the fonts listed there have a long history and would really help Fedora users of the corresponding locales. That also means a lot of them antedate recent work on free/libre licenses . For example it is common to forget about embedding.
The bulk of the listed fonts is released by foundries or individual font designers under terms not suitable for Fedora. However those terms usually only reflect the common preoccupations of font designers. They were probably not intended to prevent Fedora-style redistribution. Careful advocacy may therefore convince some authors to relicense under laxer terms that still protect them while allowing Fedora packaging.
In particular Manfred Klein may be open to a relicensing that allows distribution in OLPC through Fedora.
Fonts listed there are of high artistic quality, but have not been screened for legal or internationalization suitability.
Wazu Japan's Gallery of Unicode Fonts
Wazu Japan is not strictly speaking a free/open font directory, but many of the fonts listed there are perfectly acceptable for Fedora, and usually not listed anywhere else. Some of the URLs are stale but a little googling is usually sufficient to find the new font home.
The fontconfig defaults list many notable fonts which are likely to encountered on Linux systems. Not all of them are free/open and suitable for Fedora inclusion, but most of them are, and we've not packaged them all yet.
Stephen G. Hartke's free font list
Stephen G. Hartke compiled a list of free font resources. It includes a bit of everything: actual free/libre/open fonts, not-libre fonts (not suitable for Fedora), fantastic and not-so-great fonts. Worth a stop anyway.