Hi François,
these are my favourite freebies I've found to date:
BitterSweet3 (Flux::) Transient Shaper
BeatZille (u-he) Synth
Bx Cleansweep (Brainworx) HP/LPF
Bx Solo (Brainworx) Stereo Widener
Alchemy Player (Camel Audio) Sampler/Rompler
CamelCrusher (Camel Audio) Distortion/Amp Sim
Multiply (Acon Digital) Chorus
Saturation Knob (Softube) uh, it's a saturation knob
Span (Voxengo) Spectrum Analyzer
NoiseMaker (Togu Audio Line) Synth
Kotelnikov (Tokyo Dawn Records) Mastering Compressor
Nova (Tokyo Dawn Records) Dynamic Equalizer
SlickEQ (Tokyo Dawn Records) very slick, much EQ
MJUC jr. (Klanghelm) Variable-mu Compressor
On the paid front, I use Melodyne, some ToneBoosters stuff (great value), a bunch of SoundToys 'little' plugins, Valhalla DSP's Vintage Verb, TAL's Sampler, Kazrog's KClip, the full version of MJUC (stunning!) a few plugins by Klevgränd and SPL's De-Verb (great for knocking back the reverb on dialogue).