As one of its daily deals, Groupon offers the 3D Luxe Premium Tempered-Glass Screen Protector for iPhone 4/4S or 5 for $12.99 plus $2.99 for shipping. That's $27 off and the lowest total price we could find. This protector is purportedly engineered to a 9H hardness and tested against hammers and drills. It features anti-shatter construction, smudge-resistant coating, and more. Deal ends May 5.

Of note, you can buy two for $25.98 with free shipping.