I've tried a lot of different versions of making soap labels. And there are pros and cons to almost every type. I always made my own labels on a computer and printer, and liked the 5 to a horizontal sheet, the best. A sheet of tinted paper is 5 - 10 cents, making each paper label 1 - 2 cents plus the ink and the tape. Making labels yourself allows for you to make special labels quick and easy, like for a special occasion. The downside to this particular label is getting your cuts straight with scissors, to give it a professional look, and not like one of the kids labeled it. Then you need two pieces of tape, a 2 sided tape for the inside and a one sided tape for the outside. The inside tape will hold your label affixed after the soap shrinks a little bit more, then the label won't fall off.
But take a look at this soap label making page at natural-soap-making.com and at the variety of labels, and get some great ideas on how you could label your soaps.