I think the black grille is a no brainer, it looks really sweet on a black e9x.
Black reflectors are subtle and an easy/cheap mod that gives the front a clean look.
The black wheels are really the deciding factor. The apex arc-8 satin black wheels looks really nice. But again, might be too much black. And I imagine they are like a black car and look like crap when they are dirty.
Hyper black or gun metal might be a nice offset from all the black. The 2010 e90s don't have chrome trim on windows. It's all black.
2014 Z4 35is - Valencia Orange Metallic with Alcantara/leather Black/Orange. 326M wheels.