Soundfonts are so old...that..soundfont.com doesn't even exist anymore. Nah but I haven't used a Soundfont in awhile.
Anyways, I would start here,
http://en.wikipedia.org/wiki/Soundfonts
then
http://www.kvraudio.com/ (Great website, leading website actually)
Also... research VST Plug-ins & Instruments / Technology. Steinberg, reFX, Native Instruments, Spectrasonics, Waves, PSP Audioware, etc. These companies make great products.