Just recently, I blogged how awesome Etsy is for affordable art. Another alternative to jazzing up some blank space is to create a fabric wall hanging. Textile Arts is a wonderful shop that offers the groovy designs of Marimekko and other mid-century modern designers.
I've ordered some in the past, and lemme tell you ... they are super easy to put together. You will need a staple gun (see Nest Essentials) and a little bit of muscle to assemble them for yourself! They range from $65 to $130. Totally worth it since they are quite large (mostly over 42" wide).
Here are some other great patterns:
LEHMUS - Serene Sublimity