When I first met that guy I married, he would often disappear for hours to go play with this ENORMOUS canvas that he unfurled in the alley way behind his apartment. He would then take turkey basters filled with paint and go all Jackson Pollack on this canvas. Years later we found the canvas in the back of a closet. It was way too large to display as art in our apartment. But, with a lot of help from my mother hemming and ironing and hanging, we made these awesome custom curtains out of the canvas.
With the rest of the unused canvas, we created a custom headboard. This was just for a short time while we used our office for a guest room, so we only hung it up with thumb tacks. But if this were to be permanent part of your home decor, it'd be beyond easy to mount it on a wooden board. Maybe even add some padding to make a cushioned headboard!
If Jackson Pollock isn't your style, you could always paint a classic headboard shape on a piece of canvas. OR, if you're good with a needle and thread, you could embroider one.
Blank canvases = cheap home decor that can be ANYTHING you can imagine, much like the suggestions in our ephemeral wall decor post. So what would YOU turn your blank canvas into?