My most favourite atypical  freebie has got to be my collection of shaders, most particularly Bagginsbill's Candle Shader which I have been using in so many of my renders.  Next up would be his glass orb shader.

I have so many freebies installed in my runtimes, as well as many that I have archived "just in case" and I frequently browse through them and  install some periodically. There is no way I can pick just one out of all of them.  They are all appreciated.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi