Recently my wife sat on her reading glasses, snapping them right in the middle at the bridge.
Now, reading glasses are cheap, and occasionally breaking one isn't the end of the world. Nonetheless I found it worthwile to repair it, even just for the sake of repairing them. Besides, I love technical challenges but loathe throwing things away that could be repaired. 
The repair was relatively straightforward. Just glueing the halves together would be too week, so I took a small nail, snapped the head off which left me with a piece of wire about 15mm in length. With drill of suitable diameter, put in a pin vice (you don't want to use your power drill for that kind of work) I drilled holes about 8mm deep into each half, filled the holes with slow-setting epoxy, applied some more glue to the break surfaces, inserted the nail and pushed both halves together. Clean up excess epoxy, place the glasses on a stable surface where it will keep aligned while the epoxy is setting. 
Let cure overnight, then sand and polish. Ta-daa.