Links to SoundFonts and other similar files
To fully exploit the capabilities of SynthFont you definitely need a goof General Midi SoundFont. A GM SoundFont has presets (instruments) defined for all 128 melodic midi programs, plus at least one percussion set.
What more?

If you know of a site you think is worth listing here, then please contact me.

For a list of SoundFonts I recommend and offer for direct download, go here.
Keppy Studios by Riccardo Loi Riccardo has now a new web site with a number of SoundFonts available. Don't miss his main project, the piano only soundfont "Keppy's Steinway Piano", and some old projects like the Farfisa Grand Piano (now maintained by me) and Roland Dream Piano. Don't forget his improved Aspirin GMGS bank.
"Merlin SoundFonts"
This site does not ONLY have the Merlin SoundFonts but a rather large collection of other free SoundFonts.
Arachno by Maxime Abbey This bank includes many famous sounds from the best synthesizers by Roland (D-50, Sound Canvas...), Korg (M1, X5...), Yamaha (MU, Clavinova...), Fairlight (CMI), E-MU (Emulator), Ensoniq, and many others.
Giant SoundFont Giant Soundfont 5.5: Note that you will need to download banks 1, 2, and 3 of v5.5 as well as the drumkit which is labelled v3.0. Giant soundfont is 450 MB uncompressed, the author updates it regularly.
Sonatina Symphonic Orchestra The creative commons-licensed orchestral sample library Sonatina Symphonic Orchestra is a free library by Mattias Westlund in SFZ ("SoundFez") format. Sounds good!
Free Sound Vault "Here you can download free sound samples, soundfonts, wavs, hip hop samples, etc. for your use in music production and hip hop beat making."
Soni Musicae "Original good quality soundbanks, in different formats, mainly harpsichords and pipe organs"
Precisionsound "High quality sound samples for music production and sound effects for the multimedia/movie industry" Various formats
Soundfont Click New site by the people behind the Composition Contest site. Get the free Merlin SoundFonts here!
Jensen Samples Authentic guitar sounds. Some free SoundFont demos. By Andreas Lundsfryd Jensen.
SGM 180 A good, large General Midi SoundFont
NTONYX Some free SoundFonts
Sf2-files Free and commercial hi-end quality soundfonts in many formats
Pipe Organs Bruce Miles' 'English Organ' (Classical) and 'Cinema Organ' (Theatre)
Hammersound A classic place to go.
Sf2 midi download Quite large selection. Have a look.
S Christian Collins GeneralUser GS is a very good GM and GS compatible SoundFont
Nando Florestan Some very good orchestral SF's
Lysator This is a Swedish FTP server with mostly old stuff.
SynthZone Soundfont Resources, lots of links
Melodik Rather large list. Site is in Turkish language only.
TheJazzPage Well, eh... The Jazz Page
Johannes Roussel's site Some good stuff there
Sf2 (Russian site) Seems to be a large collection?
Helgesson The Maestro Concert Grand by Mats Helgesson
Shareware Music Machine Here you will not only find a collection of SoundFonts, but also SoundFont editors, players, and utilities.
RKHive SoundFonts ... a SoundFont archive since 1995. Here you can find some of the classic GM SoundFonts (in "Banks").
Ethan Winer's originals Ethan provides a set of original musical instruments