What are my options for closing a large gap between an incisor and canine? (Photo)

Over the years, a gap between my left lateral incisor and canine has grown, and I'm not comfortable with it. It's starting to look as though I'm missing a tooth. (I also have the same type of gap on the teeth right below, so I'm thinking this may have something to do with the way I hold my tongue.) What's the best way to fill this gap? I'm considering bonding, but I'm concerned about it falling out or becoming discolored.