French milled or hand milled: Tends to be gentler than most soaps and a bar lasts a long time. These also tend to be more moisturizing.
Triple-milled: a really dense and long lasting soap that's pressed three times to get rid of any air. The bar is hard, long lasting and lathers well.
Castille: extremely gentle soap composed of olive oil and water. It has a greenish color and virtually no trace of scent. Rich, soft, and slightly greasy, Castille soap is best for dry skin.
Glycerine or Transulcent: made from oil and the emollient glycerine. Because they are extremely mild, soft, and gentle, they are good for babies, children, and adults with normal, dry, or sensitive skin.
Super-fatted: Extra oils or emollients (olive oil, cocoa butter, even milk or cream) are added to make super-fatted soaps even creamier and more moisturizing, especially for dry or sensitive skin. They don't lather well, but that's not necessary for cleansing.
Milk soaps: milk moisturizes, softens, and soothes itchy dry skin. These are good for dry, normal, and sensitive skin.
Extra tidbit: soap will last longer if you let it sit out before using. Always unwrap bar soap and leave to "air-dry" before using. Once you've started using it, don't let your pennies wash down the drain. Get a drying rack, or dish to let the soap dry in between uses. When soap stays soft it tends to "melt away" faster.
And I have to give a little shamless plug. I make and sell handmade olive oil soap and sell it on ETSY. If you'd like to check it out go to http://www.etsy.com/shop/thehomemakerstouch