i use the micron pigma pens- they are acid free- archival quality, permenent, do not run, bleed or fade. come in a variety of colors (i have a 16 color set)
the sharpies are ok but get the fuzzy edges- micron pigma pens do not fuzz on the edges- they stay (crisp) on fabrics.
there are a number of permenent fabric markers on the market- Nancy's Notions & Clotilde's offer a variety- so do most craft stores, like Joanne's, Michaels, Hobby lobby...