A Google Site which has many different SF2 sample libraries, like Salamander Piano SF2, realistic guitars, improved versions of SGM and more. Note that some of the sounds are non-free.
A few public domain SF2 sample libraries. However, notice that some of the tones come from third party sources, for example Roland. Even though this is the case, there are still some original tones.
A few SF2 banks are available on this website. Some are public domain.
A modern SF2 library, licensed under GPLv3 with exception.
Features Roland SC-88Pro samples, 4GB in size.
This SF2 library features some SC-88Pro tones. Note that the "Natural Grand Piano" is from the SC-8850 or XV-series.
A public domain slap bass.
A compilation of some of the best libre samples. Note that some of them have a non-free license (this means a CC Noncommercial or Noderivatives license, a grey area, or even "All Rights Reserved"), but all the libre samples are quite good.
A project to build a completely libre GM SF2 sample library. Similar in purpose to Stardream Studios mainstream/large soundfonts.
Stgiga - provided many tones from HiDef, their 4gb sample bank, in older versions of Enchant!/DSOUNDFONT Ultimate.
Yingchun Soul - provided many synthesised tones from Starlight Dream.