I have a "Black Death Gun" middy upper with a S.I.R. EoTech, Pentagon light, Smith Vortex F.H. This is the "Personal Defense" upper, and general lead flinger.
I also have a 20" heavy bbl. varmint upper, with a Leupold, bipod, and a rail for a spotlight. This is a GREAT shootin rig for 'dogs, hogs, turkey, turtles (I HATE TURTLES!!!)....and yes even deer (.223....I know....

I currently putting together parts to make me an M4 type upper, just to have something a little handier to keep in the pickup while I'm at the lease.
Ar's (along w/ 1911's) are like the Small Block Chevy's of the gun world. Half of the fun in owning them is shopping for parts and then... working on them yourself