Just got my Sewline Fabric Pencil!!! ($12.95) Absolutely put this one in the TQS Treasure Chest for all to share! I purchased the white one. The eraser (on the pencil end) DOES take the marks off. And the marks also come off with water (before ironing!) Comes in a variety of colors but I can only speak to the white. LOVE IT! It works the best on a sandboard but pretty darn great without it too!
Also bought the separate Eraser Stick ($3.75) and couldn't stop there so bought the Fabric Glue Pen ($5.95) (dries clear & water soluble) Love it tooo! My contributions to "stimulating" the Quilt economy! Not in my LQS' yet -- I ordered online after seeing the Fabric Pencil given a rave review in Quilter's Home mag.