The Best Free VST Instruments - Soundfont / SF2 player:

Soundfont Player with 4 Envelopes

The KX SF2-ST plugin by Xavier Kalensky is a great freeware stereo soundfont player. The VST plugin features 4 ADSR envelopes and an LFO to modulate the amplitude, frequency cutoff, resonance, and pitch. KX SF2-ST is capable of some serious modulation (listen here for an extreme example), but at the same time it is very easy to use.

Natural Sounding SF2 Player

The free Soundfont Enhancer VSTi by Gregjazz is a SF2-player perfect for making your instruments sound more realistic by adding randomness to the signal. For a given played note, Soundfont Enhancer works by accessing the other multi-samples in other regions of the keyboard and bringing them into the sound (instead of just playing the single multi-sample associated with the note). The more multi-samples a soundfont consists of, the more realistic the sound will be. The Soundfont Enhancer VST plugin features velocity- and pitch control, amplitude envelope, vibrato, glide and legato. And it comes with several effects: eq, reverb, delay, tremolo, flanger, distortion and wah-wah.

Workhorse Soundfont Player:

SF2 v2 is a freeware VST SoundFont 2 player by DSK Music. The plugin features an amplitude envelope, a multimode filter envelope, an advanced LFO section with output routing, note bend and retrigger, portamento and delay. The free SF2 v2 VST plugin also offers a Midi channel selector and Midi automation & learn.