I have compiled a list of all the free RTAS and AAX plug-ins I could think of. The list is nowhere near as long as a free VST list would be but nonetheless there are quite a few handy plug-ins here. Needless to say, while this is an RTAS and AAX plugin list, most of them should be available in VST and AU as well.

Audiffex – ampLion Free – Guitar amp simulator.

Avid – Structure Free – Free sampler.
Avid – Signal Tools – Metering.
Avid – Xpand! – Sample-based instrument with tons of presets.
Avid – D-Fi – Lo-fi and creative sound design.
Avid/Bomb Factory – Free Bomb Factory Plug-ins – Old Bomb Factory plug-ins gone freebie.
Avid/TL Labs – TL Utilities – Metering, metronome and tuning.
Avid/TL Labs – TL AutoPan – Panning effects.

Applied Acoustics System – AAS Player / Swatches – Swatches is an ever expanding sound library for the free AAS Player.

Blue Cat Audio – Freeware Plugin Pack – A little of everything.
Blue Cat Audio – Chorus – Indeed, it’s a chorus.
Blue Cat Audio – Flanger – Indeed, it’s a flanger.
Blue Cat Audio – FreqAnalyst – Spectrum analyzer.
Blue Cat Audio – Gain Suite – Gain utilities for controlling volume.
Blue Cat Audio – Phaser – Indeed, it’s a phaser.
Blue Cat Audio – Triple EQ – A 3-band EQ.

Boz Digital Labs – Panipulator – Check your mix on bad systems.

Brainworx – bx_cleansweep – Hi- and lo-pass filter.
Brainworx – bx_solo – M/S tool.

Cableguys – Pancake – Panning modulation.

Camel Audio – Alchemy Player – Software instrument with 1GB sound library.
Camel Audio – CamelCrusher – Distortion.

Dasample – Glaceverb – Emulation of vibrations and acoustic responses of different materials.

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

Elysia – Niveau Filter – Nice filter.

Flux – BitterSweet II – Free transient designer.
Flux – Stereo Tool – What the name says.

FXpansion – Orca – Fishy synthesizer.
FXpansion – ClapOMatic – Cheering for your ego.
FXpansion – DCAM: FreeComp – A model of a classic console bus compressor design

HOFA-Plugins – ProjectTime – Measure the time spent on your project.
HOFA-Plugins – Meter, Fader & MS-Pan – Metering, fader and M/S 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 stuff, and ways to buy more.
IK Multimedia – SampleTank Free – Sample-based virtual instrument.

Izotope – VinylThe tool for simulating vinyl.

JK Plugs – JK-Pipe – Captures default Mac audio input set in System Preferences.

Klanghelm – DC1A – Easy to use compressor.

Magix – Independence Free – Sampler workstation.

Massey – Massey Tools – Various handy tools.

Metric Halo – Thump – Bass monster.

Native Instruments – Kontakt Player – Sample player for use with Kontakt Powered instruments.
Native Instruments – Reaktor Player – Reaktor for players.
Native Instruments – Guitar Rig 4 Player – Modular effects processor.

Ohm Force – Frohmage – Cheesy filter.
Ohm Force – Cohmpost – Eh… Uhm… I dunno…?
Ohm Force – Symptohm: Melohman PE – Synthesizer from the wacky french.

Pleasurize Music Foundation – Dynamic Range Meter – Metering distributed by Brainworx.

PSP Audioware – PSP PianoVerb – Strange reverb.
PSP Audioware – PSP Vintage Meter – Metering.

Softube – Saturation Knob – Free saturation… Knob.

Sonalksis – FreeG – And yes, even more metering.

Sonoma Wire Works – DrumCore Free – Drum plug-in.

SoundHack – Delay Trio – Creative delays.
SoundHack – Freesound Bundle – Various tools.

SPL – FreeRanger – Slightly crippled equalizer.

Studio Devil – Studio Devil BVC – Amp modeling.

SynthMaster – SynthMaster Player Free – A down-dieted version of SynthMaster.

TriTone Digital – MuteTone – A workaround to the inability to shut off input monitoring.

Two Notes – Torpedo PI-Free – Speaker and mic’ing simulator.

U-he – Zebralette – Synthesizer.

UVI Sound Source – UVI Workstation – Sample player.

ValhallaDSP – ValhallaFreqEcho – Frequency shifter and echo.

XLN Audio – Addictive Drums Free – Virtual drum instrument.
XLN Audio – Studio Grand Free – Free version of Addictive Keys.

Yohng – 4Front Bass – Virtual bass instrument.
Yohng – 4Front E-Piano – Virtual electric piano instrument.
Yohng – 4Front Piano – Virtual piano instrument.

Have I missed any? Let us know and I’ll add them to the list!