My daughter's bed was merely a box spring and mattress atop a steel frame. With her newly painted walls and baseboards, I felt that her bed needed a simple headboard. I used some leftover pine plywood, made legs from a 1x2 sandwiched between 1x3s, and trimmed it out with 1x4s. I painted it with the same white Duration paint that her trim was painted with and, voila, a headboard.
Everything is held together with glue. Brad nails were used to, essentially, hold the pieces while the glue dried.
"It looks almost professional," my wife said. Almost.