Karma is an extremely amusing counter for Nasus. Oh you gonna last hit that minion with your Q? Eat shield dogface...eat shield.

Riven

The biggest threat I face as Nasus top is Crit Plank. Basically I just hope that he doesn't crit with Parley, otherwise I have to use up all my HP Pots in a few minutes.

singed, poison to zone him. slows counter each other.

Renekton and Riven

I like Renekton more because it's like roleplaying on top of destroying the enemy!

From when I played Nasus, and when I played against Nasus, I usually choose someone with a spammable poke. Talon surprisingly is very strong against Nasus. And now that they've buffed him even more...

What you need is someone who can exchange with Nasus early levels. Whenever he goes in to Q a minion, fight him. This will either force him to Q you instead, or to Q the minion at the expense of a good chunk of his health. Panth is good in that he can QWE every time Nasus tries to farm his Q.

You need a strong early game champion, a champion with a spammable harass, a champion with amazing sustain, or any combination of the above.

If you let the enemy team get to 500 Q and you haven't won the game, you are bad.

Amazing

Yes, because there are so little factors in each game that you should always be able to finish before Nasus has 100 Q kills farmed up...
If the teams are even, and all but 1 or 2 champions are left after each fight (means it is a close game), the teams aren't going to be able to push those end turrets without somebody being up soon (or maybe someone on the other team escaped and is healed up and you are 40% after the fight).

But seriously, why even post that?

As for my input, a lot of the people already mentioned are pretty good to counter Nasus. I personally love Rumble against him, but a problem with that is he should be at his turret if he makes you harass him with Q so you're very susceptible to getting ganked/camped by their jungler.

Any of the typical top lanes that rely on attack speed, like Irelia, won't do well. Any champ that relies on consistent harass to eventually zone out enemies, like Shen, won't do as well. Anyone else will probably kick Nasus' butt. My personal choice is Kennen.