If you can play positionnal chess the NimzoIndian will lead to aggressive games if you play for it as black (1.d4 Nf6 2.c4 e6 3.Nc3 Bb4!?)
Otherwise the gruenfeld defense (1.d4 Nf6 2.c4 g6 3.Nc3 d5!?) lead to open and sharp middlegames (unless both players try to get into a quiet game).
The budapest defense as well leads to open and imbalanced games (1.d4 Nf6 2.c4 e5!?)
But when I want a sharp and positionnal game as black vs d4, I usually go for the clarendon court (1.d4 c5 2.d5 f5?!). This opening is objectively not good, however if white makes a few mistakes in the opening black can get a really good game with attacking chances everywhere, and since it is so unusual really few players know how not to waste moves in there. But as I said, the opening is bad, so be sure to have analyzed and being familiar with what is going on in the positions that arises before playing it, otherwise you will just end up in a passive position with weaknesses and in which white has almost no bad moves (which means really easier to play for him)
So I'm looking for aggressive lines against the d4 defenses. Any suggestions?