We stopped in at Stylelist and spotted this Flickr photo from member Justin and Elise. It's literally acorn tops glued to push pins or upholstery tacks. It's a simple craft that can dress up a space in that small handmade way that makes your friends wonder where you get the time to do such things.
If you want to dress them up one step further, try hitting them with a coat of spray paint. Bright pops of unnatural color are good as are metallics or even a bit of Plasti-Dip rubber paint. If you're in need of a tutorial you can check out Stylelist for more details.