My immediate project is a Carbine length flat top with a piston conversion kit from Adam's Arms and a Trijicon ACOG. I'm getting the barrel from Bravo Company. They have a good cold forge hammered barrel for not a bad price. Rock River's NM two stage trigger and parts kits will finish out the rifle.
The other receiver, I don't know yet. I'm toying with the idea of doing a classic 20" A2. But then Magpul is supposed to be doing a rifle length hand guard and I'd like to do the furniture that way.
Edit: Unix Jedi reminded me of something. This current AR project is all about "because I can". So, before you go all mall ninja on me about "ZOMG! The piston is the shiznitz!", or "Son, that gun was killing commie pinkos with direct impingement when you were still in diapers." Remember, the AR is arguable one of the most customizable rifles on the planet. And this rifle will be customized. So there!