Sigler Music Fonts

Features Jazz Font and Swing Font, usable with Finale and Overture. Includes demo pages, online ordering form.
http://www.jazzfont.com/

DVM Publications

Company that features some font packages for engravers and publishers: includes demos and online ordering.
http://www.dvmpublications.com/

Gregorian Chant Fonts

Featuring StMeinrad and StMeinradAux, that contain the symbols necessary to reproduce Gregorian chant.
http://www.music.princeton.edu/chant_html/fonts.html

Final Font Solutions

They offer fonts for specific tasks in music notation software like Finale: figured bass, ornaments, guitar tools, and lyrics.
http://www.ansgarkrause.de/finalfonts.htm

November

Made up of more than 330 symbols, from basic shapes such as note heads, clefs and rests, up to rarer characters like microtonal accidents, plain-song clefs or baroque ornaments.
http://www.klemm-music.de/november/index_e.htm

Handbell

By Paul A. McKlveen for the handbell notation; available in TrueType and PostScript for Macintosh and Windows platforms.
http://www.webcom.com/mcklveen/font.html

Bach, Musicological Font

[Win - Mac] Shareware font for writing essays or compiling databases which need to have some musical symbols in them.
http://www.music.qub.ac.uk/~tomita/bach-mf.html

Matthew Hindson: Fonts and Utilities

This composer offers some freeware fonts for both Mac and PC.
http://members.ozemail.com.au/~mhindson/fonts_and_utilities.html

Really Loud Font Company

[Win - Mac] Description and order form for their font collection.
http://hometown.aol.com/LoudFonts/Home.htm

Sonata

[Win - Mac] Description and order form for this font by Adobe.
http://www.adobe.com/type/browser/P/P_021.html

G. William Music Production, Inc.

Offers a collection of fonts created by composer Bill Duncan. Samples available.
http://www.gwmp.com/MusicFontsFrameset.htm

Caltabiano: Music Fonts

Offers Sicilian Numerals, Ghent Percussion Font, and Rehearsal Letters. Samples and order form available.
http://www.caltabiano.net/shareware/index.html

Express Music: Fonts

Offers three music fonts: Ashmusic, Leemusic and Russmusic. Available for both Mac and PC.
http://expressmusic.com/

FacSimilus

Sibelius and Finale fonts including figured bass, common and special symbols, ornaments, special and straight lines.
http://www.facsimilus.com/FacsimilusFontFamily/en/Default.aspx

Toccata and Fughetta

Two fonts designed to be used with Finale. Includes samples, free demos, and ordering information.
http://www.efn.org/~bch/AboutFonts.html