There are a whole pile of free effects out there to download to help you in your mixing. Here is a list of plugins I have tested and use regularly:
MJUCjr – as many plugin makers do – Klanghelm release a cut down version of their more complex MJUC Vari-Mu compressor plugin for free. Simple, easy, vintage style compression with two main knobs and sounds great.
Acustica Audio are makers of high end effect plugins. Using a different technology from most plugin creators (they sample every parameter of existing collectible studio hardware using convolution) their commercial plugins are expensive and require a lot of processing power.
To give you a taste of the wonders of their wares, they have a selection of free plugins available. If you sign up to their Aquarius system (free), there are a couple of EQ’s and a compressor – all sound fantastic, but you wouldn’t put them on every track in your session if you want to save your CPU.
“Coffee – the PUn” from Acustica Audio is yet another Pultec EQ – but probably the best sounding version available, and it’s free!