My roommate only uses shampoo--Suave. It's cheap and cuts down on the number of products a person has to use. It's not really any different than just using liquid castile soap (like Dr. Bronner's) for everything.
We use Neutrogena Rainbath gel. Since we share a shower with two roommates, leaving a bar of soap in the shower is not a great idea. It tends to get icky fast. As for shampoo--I switch off between using Paul Mitchell products and whatever salon-grade product I can pick up cheaply at the Grocery Outlet. I'm pretty good at scouting out deals on salon shampoos and conditioners. Right now I've got two enormous bottles of Paul Mitchell shampoo and conditioner from my salon that I picked up; they were a really good deal at $13/ea. It still costs more than Suave, sure, but I can't use Suave or many other cheap shampoos; the detergents are too irritating to my skin and make my face break out in a terrible rash, not to mention my hair frizzes out. Ugh. I will always splurge on hair products, though I always try and find the best deal for my hair products. I love a good score--like the Paul Mitchell foaming pomade that I picked up for $4 because it was on clearance
