Hm, let's see who counters Darius, shall we?
Jayce, Teemo, Fiora, Irelia, Jax, Malphite, Yorick, Ryze(for the trolling top lanes), Swain, Kayle, Trundle, Voli(pedo)bear,Vi, Free Wi- I mean, Lee Sin, Akali... Gee, I think I just named over half of the toplaners I know to be used.
For melee champs, oh boy, is Darius pulling you? Cute. Bash his head in with Jax's street lamp. Hiten Style and out-sustain him with Irelia. Yorick obviously has almost no counter. Voli has a fling and a fear attack. Vi punches Darius. Lee Sin + Cripple = death. I could keep going, but I'll leave it there.
And don't even talk about the ranged toplaners.