DIY canopy: 2 curtain rods and 2 sets of LILL sheer curtains, (all from ikea). Mount one rod on the ceiling, and the other on the wall. "Swoop" to your liking. I finished it off with lights (also from Ikea), and a fluffy Ralph Lauren duvet, (thanks mom).
If you're a little short on fabric, try making a paper garland to use as a window topper. Paula from Counting Your Blessings strung pages from vintage books onto ribbon, bunching them tightly to create a fluffy, unique and inexpensive valance.