Just look at those baby faces!
The Angel was a game changer, much sleeker and slicker than anything else available. The Ion brought electros to the masses despite it's questionable build quality it still remains a fantastic platform, and challenged all the other manufacturers to introduce mid-range and starter price-point elector markers to the market. The Halo was a reliable and fast loader capable of keeping up with guns capabilities for the first time, often imitated, rarely bettered (not until the advent of the Rotor really).
But probably the biggest one ever: Gel encapsulation technology!