I just finished reorganizing my yarn stash, which has made me curious about how others organize theirs. I had sorted it out by fiber - silk in one bin, cashmere in another, cotton/linen/cellulose fibers in another, etc. Then I realized that 90% of the time, I select the yarn first based on the size, THEN by fiber content - also that fiber content isn't a really accurate way of storing things because what do you do with blended yarns? So I reorganized my stash by yarn size - 1 bin for 20,000 ypp and finer, 1 bin for 10,000-20,000 ypp, 1 bin for 6,000-10,000 ypp, 1 bin for 3000-6000 ypp, and 1 bin of anything heavier than 3000 ypp. (Plus one bin of rayon and cotton chenille, because I've got enough of it to fill 1 huge bin, and one bin for 30/2 silk, because I have 10 kg of it!) The only thing that is still separate is my linen/cotton/cellulose yarns, because they fall into a different dye class than everything else.
It's also easier for me to index my yarn this way because in my yarn database (yes, I have a yarn database - I'm such a geek!) things are sorted by weight, and that way I can always find the right yarn without rooting through everything.
I don't sort by color because everything's white! I dye my own as I need it, so probably 90+% of my stash is white.
How do YOU organize and keep track of your stash?