Guests throw darts at balloons with paint inside. You keep the art. :) This is such a fun Idea. You choose the colors and the size to coordinate with your style - might be more enduring than having a fingerprint tree in your house forever.
Chalkboards are extremely trendy right now! To give your guests something sweet to read, display a relationship timeline chalkboard. If you want to make your own chalkboard, you can purchase chalkboard paint at a majority of craft stores.
Make one special photo charms for you, compatible with your Pandora bracelets. Beautiful wedding photo with an artistic touch, featuring the wedding couple in silhouette (via Awesome Photography - People and Portraits / shadow)