If you like tactical games, the Sicilian offers lots of sharp lines against 1.e4. You could also play the French Defense, Winawer variation if you don't mind possibly losing a kingside pawn or two to get an attack.
1.d4 tends to be more positional, but if you want an imbalanced game you can play the somewhat eccentric Dutch Defense with 1. ...f5 and then choose from several variations. The most common are the Stonewall, which is somewhat more positional but can easily become tactical, and the Leningrad, which is a throw-caution-to-the-wind line and tends to be very sharp unless both players are overcautious.
1.c4 and 1.Nf3 are also common enough to worry about, but generally you can use a Dutch- or Sicilian-like system without too much trouble, or just follow a classical development plan by using 1. ...d5/e5 and moving pieces out normally.
Almost all of my opening repertoire includes openings and attacks for white, but I have nothing prepared for when I have to play Black. What do you recommend me?
I'm better at tactical games than at positional ones, and my opening repertoire as white is basically made of 1.e4 openings:
Oh, and don't be afraid to say "dubious" lines, I've already tried the Latvian Gambit, the Halibut Gambit, the Fried Fox and some others.
Thanks in advance!