Scattered around my audio production drives, I have hundreds, perhaps thousands of free soundfonts, acquired in an addictive frenzy from 2003-2006.    Eventually I stopped looking for new soundfonts, because I had invested in better commercial libraries.

A few soundfonts, however, have stood the test of time…. these are ones I return to for one reason or another.    

FARFISA ORGAN
This is an electric organ… a cheap, trashy home transistor thing.   Sometimes it’s just the ticket.

Rhodes VS Extreme
This rhodes sample set has a unique mellow tone that I haven’t found anywhere else.   The samples are from a Rhodes MKI 73 Stage Piano. 

FLUID Release 3 GM
When you absolutely need a glockenspiel, or some tubular bells, or a wood block… or a gong… or an 808 kick, or well, anything.. you’ll find it here.  These samples aren’t going to floor you with their quality, but they are surprisingly useful in a mix, like the on-board sounds on an old Roland sampler.

Zvon Prepared Rhodes
There’s really nothing like this… it’s based on John Cage’s experiment where he muddled with the inner workings of a piano to create new sounds and percussive noises.  You have to hear this to believe it… Zvon recreated Cage’s work on a Fender Rhodes, and created a soundfont.  The light version is basically free (it’s only $2).    The full version is $20. 
http://www.lesproductionszvon.com/zvon_PR.htm