I've always liked
the classic, traditional look of painted wooden beadboard. It can be installed on ceilings or on walls as a wainscoting.
Beadboard is widely available (Dyke's Lumber has it) and you can install it yourself. It can make a space feel cottage-y or victorian.
Bead board was traditionally used as a finish material on the ceilings of victorian porches. It is sometimes used to soften up bathroom spaces and I especially love the abundant use of the material in this small space on the left.