Something for the bottom, like a BN Plec
I've always liked mollies / swordtails - but in 75 gal, you could get a hell of a lot of guppies, all with different colours - they'd swim around the main body of the tank, so then you'd have danios on top, angels and guppies in the middle, and a BN plec or maybe even some cories for the bottom!
You could always go for some Clown loachs, they add colour to the bottom and have quite a bit of character, and also in a 75gal you could get one hell of a lot of tiger barbs - which would look fantastic, and cut down on the agrression!!
One last idea - you could get a couple silver sharks (bala shark), they look amazing, do well in big tanks - and I don't think they would bother anything else you've got in there!
hope at least some of this rant helps!
EDIT - Forgot Gouramis - you could get a few nice looking gouramis, like a group of them, to add colour and a bit of a different size fish!