If you're counting the days in your house, this advent calendar found over at Lovely Things is one charming way to do it. It's the most fun and creative I've seen. And loving the entire gorgeous vignette created around it. But it would still be an inexpensive and easy project. If you're inspired, go to it!
If you're looking for more diy decor, Pewter + Sage's pinecone garland struck me as so simple and perfect. A little bit of time outdoors gathering pinecones and half an hour wrapping twine and you're done. My kind of project.
I also love My Many Moments mossy twig wreath, another simple, inexpensive (actually free!), rustic diy.