Artwork. For my money, it's the number one way to add personality to a room. Sure, a $25 can of paint can make a big impact, but I'll take a white room with loads of art over boldly painted walls any day.
But, of course, you can't just go to the artwork store and scan the aisles until you find just the right piece of scale and color that matches your decor. Real art takes time to create, and fetches appropriately not-cheap prices, and isn't widely available at the local shopping center. Sure, family photos are nice, and an artfully framed poster will do, but don't you dare head to that kitchen and bath supply shop and paw through the faux-Tuscan paintings.
Instead, make your own. Quickly, easily, inexpensively, and no artistic ability required. I whipped this one up for a series of posts sponsored by Krylon on our sister blog, Curbly. Get the full instructions there!