My stiletto. I don't just use it for piecing. I also love it at the iron to keep my fingers from getting burned while pressing seams open (like the hundreds of small wedges I just made).
My newest favorite gadget is my batting scissors. Didn't know how much I needed them until I bought them. The handle is curved up from the blades and the tips are blunt. Can cut that batting so easily without getting the scissors caught in it.