You know that little bag of magnet rocks you bought at the science museum that seemed so cool at the time, but you promptly forgot about? Go dig it out of whatever cold, dark corner it's hiding in. Those magnet rocks make awesome fridge magnets. They hold better than any of my "real" fridge magnets. Plus, they look really cool on your fridge.
Bonus tip: Check if your front door is magnetic. This was one of the most awesome discoveries in our apartment. It basically triples our "refrigerator door" space!