There are several manufacturers of pistons for usgi spec cylinders. Some are TiN coated some are not.
Sadlak has their normal pistons that are coated and the "NM Grooved" . This piston has a specific purpose and is not a standard NM upgrade. It's purpose is to operate with bullets weighing over 176gr. So unless that's yer plan, stay away from the "NM grooved" pistons.
Otherwise, unless you prefer a certain manufacturer, you some choices out there, other than sadlak. As H20 Man mentions, smith enterprise makes some awfully nice pistons

, check brownells for availlability.
And for those who are gonna ask, NO these american made pistons are NOT compatable with MOST chinese cylinders.