I'm building up quite a stash of threads. Mostly they're cottons for piecing and quilting, but I've recently added a whole heap of QA polyester embroidery threads. They were recommended by a professional quilter, and came in packs of 14 x 1000m spools for under $20 - bargain! Although it's not the best for finding and reaching what I want, my threads are now in (and have filled!) this 20L tub.
My favourites are King Tut, but unfortunately most of their threads (including the variegated threads I really love) are 40wt, and my machine clearly prefers 50wt for FMQing. So I'm trying the King Tut 50wt and a selectio of Aurifil as well. I also have a stack of Guterman; mostly black white and a few creams/neutrals for piecing. But that's 50wt, and I'm going through oodles of the white to do the McTavishing. Just one of the tree wallhangings used about 500m of thread in the quilting!