Dutch magazine 101 Woonideeen's website features this photo of a unique bedroom idea. Mount a string of lights to the wall above your bed as a visual (and bright!) alternative to a headboard.
After tracing your design on the wall with masking or painters' tape, use cord clips (like these) to fasten a string of LED lights (or any other lights) along the tape outline. Remove the tape and voila! Fake headboard! You can read the full DIY instructions on 101 Woonideen's website (translation here).
The outline of a headboard — in this case, one shaped like a gabled roof and chimney — is enough to frame the bed visually. And as a bonus, a string light headboard can double as a nightlight if you like to read or knit before bed.