Just started my build.  first, I have a set of matched Anderson receivers.  They actually fit together pretty tight with very little wiggle and looked very nice on inspection.  My current issue M4 has much more wiggle and I've shot expert with it.  As you can see, for those who like the black gun black, the finish for both match almost spot on.

http://i7.photobucket.com/albums/y277/David665/AR15/UpperLower1.jpg

The lower I got local for $60 and the upper is a blemished stripped that I got from Copes Distributing for $42.  The red arrow in the pic below shows the only flaw I could find.  I originally thought it was just packing clutter, as the receiver had a fair amount.  I plan on painting the gun, so this small blemish is mochs nichts.  The dust cover, forward assist and charging handle are a DPMS set I snagged from Amazon.com for $30 and seem Mil-Spec.  The forward assist I installed on my dinner table with a 4 oz. claw hammer and 5mm punch.  I went in from below and you can see the little ding I put in the receiver just to the left of the roll pin.

http://i7.photobucket.com/albums/y277/David665/AR15/UpperLower.jpg

I have a USGI carry handle on the way I got from the EE and I think the next item on the list is a PTac MOE LPK from Palmetto State, in OD Green.