We recently ran an article about the "claw" rear sights from Rob Pincus and AmeriGlo. Here's some more more information and review material on 'em.
Video from Downrange Firearms Training, http://drftraining.com/
"Claw sights are the most aggressively designed rear sights for one handed emergency manipulations in a worst case scenario. Designed with a wide .180" notch for fast front sight acquisition when you need sighted fire and a concave leading edge, The Claw will serve you well as a Defensive Pistol Rear Sight until you need it most... That's when it could save your life. Claw rear sights can be used with standard height and width front sights, including factory fronts, or paired with high visibility options. Claw Emergency Manipulation Rear Sights are manufactured in the US by AmeriGlo..."