As soon as I get a chance to redo a bathroom or kitchen, I am going to work in subway tile and dark grout.
This style is called "subway tile" because it was used in the New York City subway stations in the early twentieth century. It is simple, classic, and inexpensive. It does not have to be paired with dark grout, but I like the added geometry of it. And I think it would be great for a bathroom because dark grout can hide a lot of scum.
Note: DIY sites say dark grout can highlight sloppy work, so don't phone it in.
Jeffrey Alan Marks used this look on the show Million Dollar Decorators when he redesigned the bathroom of his Crossfit gym. He said he likes the look because it reminds him of a 50's locker room in a boys prep school.