For cold weather I made these Tapi socks(Ninja style) out of some old black ankle sports socks. They work great to wear with my Invisible Shoes(huaraches) or when I am biking to work in sub degree temps.
Here is how I made them: Turn the socks inside out and put them on. With needle and thread, stay stitched a V in the area between the big toe and other toes. Take them off and clip the channel. Serge them(or zig zag stitch) on a serge maching/sewing machine. Turned then right side out and VOILA!