Top lane, Irelia, Jayce, are safe aggressive picks. If you just want to have fun you could play assassins like Akali who are obviously extremely aggressive but at higher levels of play can be hard to use properly if other team has oracles, a lot of cc to keep you in place when you dive on them, or smart and just focus you down first.
As for Mid lane I would recommend people who have good wave clear and strong roam potential, such as Ahri or Gragas. Both have amazing mobility to quickly gank lanes and are fun to play.
Junglers, I would recommend gank heavy junglers like Maokai, Lee sin, Skarner to some extent
As for AD carries, there is minor aggression you can do outside of your lane phase due to AD carries being the weakest champions without items, but late game you will have a lot of fun. For a aggressive bot lane, go Leona, Blitz, Taric, Sona with the standard AD's Corki, Graves, Ezreal