For me still at the top of the list: Surge - incredible that this synth powerhouse is free!
Also pretty useful: OB-Xd - while there are pretty tasty paid-for Oberheim options available, this one isn’t so far off, at least for the mainstream sounds. Not 100% identical with the original (e.g. on filter sweeps), but a great free option to get one’s hands dirty on an Obie-style synth.
The Tokyo Dawn stuff is definitely nice - I just don’t use it in my Cantabile setup, since most of their plugins introduce significant latency. But for production, definitely a plus.
Other very useful free stuff:
- For guitarists: take a look at the free Mercuriall offerings - great pedals in there
Ignite Amps also have some good free stuff - NadIR is a very useful convolution host for cabinet IRs, and PTEq-X is to me the best free Pultec EQ out there
Variety of Sound has a broad range of free plugins - and they are in the process of moving all of them to x64, which is a definite plus - I don’t want any legacy 32 bit plugs in my arsenal; just one more thing that can go wrong…