Shampoo and conditioner
Shampoo and conditioner come in bar form, just like soaps! There are lots of brands out there. So far, I like Bottle None and Skipping Stone. I was very skeptical at first about how expensive they are compared to how small the bars are. However, they last a really long time (honestly) and I do think the cost is justifiable given how many uses they provide.
The results are pretty good overall - my hair might be a little less smooth these days, but not a huge difference. I do really enjoy not having to try and squeeze the last bits of liquid shampoo and conditioner out of a bottle.