DIY Balloon garland - much easier and cheaper than buying those specialty arches or helium (these colors are right on, too!)
One of the best party decorating ideas ever--hanging balloons, LOTS of balloons, from the ceiling. My husband and I recently decorated our knotty pine room in a similar manner for our son's graduation party. I know awesome is a seriously overused adjective, but it best describes how our room looked, and still looks, two weeks later. Note: You'll definitely need to buy a balloon pump for this project.