Troy announced several AR-15 receiver enhancements earlier this year. One of those enhancements is their Ambidextrous Magazine Release which is now beginning to show up at online retailers.
It is basically a small button that levers against the receiver to drop the magazine. It is supposed to replicate the feel and location of the right side magazine release button as closely as possible. You can see in the picture below that it is sized in such a way that it should be relatively easy to hit without being prone to snagging. This looks like a worthy upgrade for lefties or for anyone who needs to be able to operate their weapon with either hand.