Here's my list:
Barrel: Colt M4 SOCOM, ABS SS/ Carbon Fiber, Lilja & Noveske
Upper: Colt M4, KAC, LMT MRP & HK416
Lower: Colt rare A2 with small pivot and FCG pins, KAC & LMT
Other components:
Knight's Armament Co. URX2 & Larue Tactical FF rails
Tango Down, KAC and Magpul rail panels
Magpul ladder rail protectors
Tango Down & KAC VFG
KAC rail sling mount
BUIS: GG&G, KAC, Larue, LMT, Matech & PRI
PRI Gas Buster CH
Colt M16, Young Mfg & JP BCG
D-Fender & Crane O-ring
KAC, Jewell & JP match trigger
KNS pins
Norgon ambi magazine catch
JP adjustable/ reversible selector
Enidine hydraulic recoil buffer for rifle/ SPR length
MGI rate reducing buffer for carbine length
Magpul MIAD grip & Tango Down Battlegrip
Genuine original Crane, NOT LMT, SOPMOD stock (about $400), Vltor & Magpul M93B or future replacement model
GI high quality Teflon finished magazines
Magpul followers and plates
Wolff AR springs set
Optics: Schmidt & Bender, NightForce, Leupold, ACOG with J-Point, Aimpoint M3 & EOTech
Mounts: ARMS, KAC & Larue Tactical
There are other great stuff out there that I didn't mention.
Do it the ARFCOM way get everything.