I have many different seam rippers, but my very favorite is the surgical seam ripper from Clotilde ($3.98). It is stainless steel, about 4" long and is razor sharp. Was made to rip out serger stitches, but it is great for ripping very tiny stitches. There is also a version with a wooden handle, by Quilting Resources (I also have this), but it is much longer.