LUSH makes awesome shampoo bars, the point of them is they make no plastic waste with bottles and whatnot, and they last thru around 60 washes? They save some space too because they are pretty tiny. To use you can get a lather in your hands or rub in on your head a little, great for travel!
A lot of us use soap or shampoo bars on our hair. For the most part, it's handcrafted soap made the "old fashion" cold process way--lye is used to saponify oils and the resulting product is soap. Jillipoo interviewed me about my use of soap bars for the Daily Curl blog. Here's the link through nc.com: