Ragnarok Scriptorium Ragnarok sells a package of several uncial and decorative fonts based on Celtic manuscript hands and decorative knot and spiral fonts. Both Macintosh and Windows are supported.
P22 Kells Font P22 sells a package of several uncial style fonts based on the Book of Kells and similar manuscripts, and fonts for making Celtic style borders and decorations. Both Macintosh and Windows are supported.
Gaeilge TrueType Font Essentially a Roman alphabet, Gaeilge is a TrueType font with extra characters and diacritics for use with Gaelic. It is the type face used in books printed in Ireland until just a few years ago; there are some minor differences between it and the normal Roman or English alphabet. This font was made by father Padraig McCarthy.
The BigTed Celtic/Gaelic TrueType Font page A page of links, including one to download American Uncial, a Windows TrueType font in .zip form.
Vintage Type Vintage Type sells Vintage Celtia(TM), a family of fonts with spirals, keys, and knotwork. The fonts are available as both postscript and TrueType for Macintosh and Windows.
The SMO Gaelic College Gaelic Script Fonts This page has links to both Macintosh and Windows fonts, including commercial and free fonts.
Dr. Berlin’s Gaelic and Ogham Typefaces Howard Berlin offers Windows Ogham and Gaelige, and other medieval style faces for Windows. This is a good site for non-Latin and international Windows typefaces in general.
Clófhoirne Oghaim Ogham Fonts
Another great site from Michael Everson, the authority on Ogham as typography and the Unicode Ogham standard.
The Macintosh Font Vault A nicely organized and displayed page with commercial, free and shareware fonts. There are several medieval and Celtic fonts here; browse a bit in the Artsy and Script categories.
Windows Celtic and Medieval Fonts This site has a wide range of both decorative fonts and letter fonts, including several modeled after manuscript hands.
Feórag’s Free Stuff This is a collection of free Mac Celtic, medieval, manuscript style fonts for the Mac. Notice the Celtic interlace style desktop patterns too.
Con Kennedy’s Celtic Mac Fonts Some lovely Mac only, for now, fonts, in several variants of the Uncial lettering style.