I'm far from a purist,but nothing beats vinyl!!!
You can go to trift store and buy wax 1$ a pop.This place I go to has sleeveless 45's at 0,10$ each and I found great stuff like War,some Guess Who and other obscure ish.
This is my foundation,but I'll get samples from anywhere if it's the tv,cd's or mp3's.
But man,diggin is fun especially when you find a cheap records with a bunch of samples on it!!
Can you bake a cake w/ some dirt, tree bark and rain water?
Or do you need to go BUY flour, sugar, eggs..etc.?
That isn't to say that some free sounds aren't good... but the time it takes to listen to all the ****ty sounds to find a good one could be better spent making music