Top row, left to right:
1. Here's a clever idea: turn an antique mantelpiece into a headboard. This picture is from Apartment Therapy contributor Leah Moss' home; here's a step-by-step tutorial on how she did it.
2. Paint the wall behind the bed with chalkboard paint...and then draw a headboard on the wall. Clever, stylish, cheap, hilarious. From FlyChicks.
3. From Better Homes and Gardens: oversized mirror as headboard.
4. These Blik wall decals are super affordable (this one starts at only 40 dollars), and all you have to do is stick them to the wall.
5. Hanging an interesting textile behind the bed is a lovely (and effective, and super-simple) way to DIY a headboard. This example is from Dean's house tour.
Bottom row, left to right:
6. The very simplest of DIY headboards...just a square of color painted on the wall. So clean and modern. From Alexandra Angle Interior Design.
7. Antique doors as headboard from Apartment Therapy.
8. Here's one from Country Living made from old louvered shutters. (Being a frequent visitor to antique stores myself, I can tell you that these things are a dime a dozen.) You can sand them down and paint them any color you want.
9. A canvas with string lights behind it gives the bedroom a dreamy, fairylike feel. From Apartment Therapy.
10. And I couldn't resist including at least one headboard made from recycled wooden pallets. This one's from Stylizimo.
(Images: As credited above)