Free VST and RTAS Instruments

E-Mu Proteus VX (Mac and PC) [excellent]
http://www.emu.com/

Independence Free (Mac and PC) [2Gb of sounds]
http://www.yellowtools.us/cp21/cms/index.php?id=842

Free Alpha 3 (Mac and PC)
http://www.linplug.com/Download/download.htm

UVI Workstation (Mac and PC)
http://www.uvisoundsource.com/uvi-workstation/article_info.php/articles_id/8

Sonik Synth 2 Free (Mac and PC)
***removed from site*** wtf?

SynthMaster Free (Windows Only)
http://www.kv331audio.com/downloads.aspx

MinimogueVA (Windows Only)
Arppe2600va
http://glenstegner.com/softsynths.html

Angular Momentum Bundle (Windows Only)
http://www.amvst.com/index.php?name=Downloads&c=5

Xpand! (Mac and PC) protools only*
http://www.digidesign.com/index.cfm?navid=109&itemid=4784&langid=1
Structure Free (Mac and PC) protools only*
http://www.digidesign.com/index.cfm?navid=175&itemid=5223

Remedy (Mac and PC)
http://www.keytosound.com/?desired_section=downloads

FineLine (Mac Only)
http://cascom.se/kl/plugins/fineline.html

JK FluidsynthHEX (Mac Only)
http://www.sonoria.pl/jk/pluggox.html

Kore Player (Mac and PC)
http://www.native-instruments.com/index.php?id=koreplayer

DSK Bundle (Windows Only)

-ElectriK GuitarZ
-BlueZ
-RhodeZ
-SaxophoneZ
-BassZ
-AkoustiK GuitarZ
-Analog MatriX
-Indian DreamZ
-Ethereal PadZ
-Virtuoso
-Chaos Theory
-DrumZ AkoustiK
-OranZe
-Darkness Theory
-Asian DreamZ
-DrumZ BeatVoiZe
-AkoustiK KeyZ
-MachineZ
-SixSenZe
-mini DrumZ
-Odisea
-ThoR
-PleyadeS (beta)
-Harmonica (beta)
-KaoS (beta)
-Stings
-DreamZ
-XXX
-Brass
-ZetH
-ZitH
-ElektriK Keys
-B3x
http://rekkerd.org/dsk-vsti/

Broomstick Bass (Mac and PC)
http://www.bornemark.se/bb/downloads.htm

Rock Synth
http://www.concretefx.com/Rock.htm

4Front Bundle (Mac and PC)
-Piano
-Bass
-E-Piano
http://www.4front-tech.com/proaudio-download.html

Steinberg Virtual Bass (Mac and PC)
http://www.steinbergcanada.com/support/freeware.htm

NovaKill bundle (Windows Only)
-ANGSTkILLERmini
-COLDkILLERmini
-BRAINkILLERmini
-DREAMkILLERmini
-NEOkILLER X2
-HOPEkILLER X2
-BALLTEARER
-PISSCUTTER
-RIPSNORTER
http://www.novakill.com/killerz.htm

Tons of stuff here too.
http://www.soundfonts.it/

Nx-Sound.de - nX-Synth 2
http://nx-sound.de/index.php?option=com_content&task=category&sectionid=5&id=15&Itemid=31

Mokafix - Tatapoum 4.0 pattern based drum machine
http://soma.asseca.com/wiki/Tatapoum/LatestDownload