Caseology Legion ($16)
Caseology makes some pretty great cases that aren't too thin, but not too thick either. A perfect middle ground between most options on the market. You'll get more protection than most, but only pay a few dollars more, instead of $30-$40 like those other popular brands.
The Caseology Legion series is our favorite. It's a slim dual layer case design with polycarbonate plastic and soft-shell TPU corners. You'll enjoy a nice two-tone finish on the back with a faux carbon fiber design. Get it in one of five different colors.