Free Plugins: The Ultimate List (VST, RTAS, AU, AAX, etc.)

Audifex - ampLion Free - guitar amp simulator

Avid - Structure Free - sampler
Avid - SignalTools - metering
Avid- Xpand! - virtual instrument
Avid - D-Fi - low-fi sound design
Avid - Bomb Factory plugins - various free Bombfactory plugins
Avid/TL Labs - TL Utilities - tuning, metronome, metering
Avid/TL Labs - TL AutoPan - panning effects

Blue Cat Audio - Free Plugin Pack - a little of it all
Blue Cat Audio - Chorus - chorus
Blue Cat Audio - Flanger - flanger
Blue Cat Audio - FreqAnalyst - frequency analyzer
Blue Cat Audio - Gain Suite - gain utilities for controlling volume
Blue Cat Audio - Phaser - phaser
Blue Cat Audio - Triple EQ - 3-band EQ

Brainworx - bx clean sweep - hi and low-pass filter
Brainworx - bx solo - M/S tool

Cableguys - Pancake - panning modulation

Camel Audio - Alchemy Player - virtual instrument with 1G sound library
Camel Audio - CamelCrusher - distortion unit

De La Mancha - FMMF - user-friendly FM synthesis

Desample - Glaceverb - vibration and acoustic response emulator

DDMF - Colour EQ - EQ with custom-made 4th order IIR filter

Elysia - Niveau Filter - a handy filter tool

Flux - BitterSweet II - transient designer
Flux - Stereo Tool - stereo shaper/designer

FXpansion - Orca - virtual synthesizer instrument
FXpansion - ClapOMatic - virtual crowd/clapping simulator
FXpansion - DCAM Free Comp - a model of a classic console bus compressor design

HOFA-Plugins - ProjectTime - measures the elapsed hours of work that went into individual projects
HOFA-Plugins - Meter, Fader & MS Pan - metering, fader and MS decoder
HOFA-Plugins - Goniometer and Korrelator gonio and correlation metering

Human Touch Technology - SIKA Oriental Scale - SoundFont player dedicated to Arabic and Oriental scales

IK Multimedia - AmpliTube Custom Shop - amp and FX simulation
IK Multimedia - T-Racks Custom Shop - lots of helpful plugins
IK Multimedia - SampleTank 2.5 - virtual instrument

iZotope - Vinyl - vinyl simulator

JK Plugs - JK Pipe - captures default audio input set in System Preferences

Klanghelm - DC1A - user-friendly compressor

Magix - Independence Free - sampler workstation

Massey - Massey Tools - various helpful plugins

Metric Halo - Thump - extreme bass modulator

Native Instruments - Kontakt Player - sample player for use with Kontakt instruments
Native Instruments - Reaktor Player - virtual instrument
Native Instruments - Guitar Rig 4 - modular effects processor

Ohm Force - Frohmage - a nifty filter device
Ohm Force - Cohmpost - a very bizarre, filter-ish plugin
Ohm Force - Symptohm: Melohman PE - virtual synthesizer instrument

Pleasurize Music Foundation - Dynamic Range Meter - metering tool

PSP Audioware - PianoVerb - a strange reverb unit
PSP Audioware - PSP VintageMeter - metering tool

Sonalksis - FreeG - metering tool

Sonoma Wire Works - DrumCore - virtual drum instrument

Soundhack - Delay Trio - creative delay effects
Soundhack - Freesound Bundle - an array of helpful tools

SPL - FreeRanger - EQ unit

Studio Devil - Studio Devil BVC - amp modeling

TriTone Digital - MuteTone - a workaround to the inability to shut off input monitoring

Two Notes - Torpedo PI-FREE - mic and speaker simulator

U-he - Zebralette - virtual synthesizer

UVI Sound Source - UVI Workstation - sample player

ValhallaDSP - Valhalla FreqEcho - frequency shifter and echo unit

XLN Audio - Addictive Drums Free - virtual drum instrument
XLN Audio - Studio Grand Free - virtual piano instrument

Yohng - 4Front Bass - virtual bass instrument
Yohng - 4Front E-Piano - virtual electric piano instrument
Yohng - 4Front Piano virtual piano instrument


(Let me know if I missed any!)