If you feel the need to replace components in order to get a "two-stage" trigger, I recommend the Rock River or CMMG drop-in non-adjustable trigger kits.
I run a RRA NM 2 stage, and it is great! It is very crisp and very light, but not so light that anything but an intentional pull will set it off. I would recommend considering that depending on if your AR is just benched for shooting groups or if it might ever be employed as a defensive weapon...
All the other posters listed some really great triggers.
My Geisselle malfunctioned during the Nationals. It doesn't get a second chance.
I have several RRA service rifle triggers. They are all two stage. First stage is 3 1/2 pound and the final stage is 1 1/4 pound. Outstanding trigger. Only way to get a safe 1 1/4 pound final trigger weight.
I have two modified RRA Service Rifle triggers that I use in my match and varmint rifles. They are easily modified for a 3 1/2 pound total and 3/4 pound final weight.
All of my triggers use Wolf extra power hammer springs for a noticeable decrease in lock time.
If you think I am a fan of RRA triggers, you would be correct.