I may as well take this moment to share my favorite opening: The Grunfeld defense. It's really fun to play.
The Sicilian (Dragon Var.) is too tactical for my taste, but you may enjoy that as well.
As white, I'm a huge fan of most things resulting from d4, but especially look at queen's gambit, anti-nimzo-indian and catalan.
If all of those are too in-depth, the others have suggested some great ones: The Scotch, many gambits and some lines involving knight move as the first move (Reti and KID particularly).
The Sicilian (Dragon Var.) is too tactical for my taste, but you may enjoy that as well.
As white, I'm a huge fan of most things resulting from d4, but especially look at queen's gambit, anti-nimzo-indian and catalan.
If all of those are too in-depth, the others have suggested some great ones: The Scotch, many gambits and some lines involving knight move as the first move (Reti and KID particularly).