Charging handles... I have VLTOR BCM Gunfighters Mod 3 and love them, but I just tried a Raptor and may be sold on theirs here on out. I am also looking at the Fortis Hammer though for a pistol build.
The rest of the Upper depends on if you want to Free Flat the rail, and if you want fixed or fold up sights. FF rails typically cost more (UTG Pro is a nice budget rail that is not too heavy), but this also depends on taste. I also have a Spikes Rail (BAR),and a Midwest Industries SS Gen 2 that is really light. The lighter they are, the more they cost though. Strike Industries has a new Rail and other stuff that is pretty cool. I like the Cobra angledforward grip they have.
I just tried the UTG Pro on my Rock River Operator and I love it. Smith and Wesson M&P tactical rifles use this same rail, or have. Optics is a whole other area to get into. Primary Arms has good deals and fast shipping.