I've been hearing that top lane in draft can be really easy to counter-pick, and I'd like to expand my stable of top laners.

Who counters each of the good top champs best?

I'm currently learning Riven. She seems specifically designed to kill Nasus, but gets raped by GP; so I'd really like to hear a good counter for GP to start.

GP is just in general a real good all arounder, though rumble basically shuts down any lane most the time so maybe him? Flat out countering really REALLY depends because of jungler ganks and what not

I assume this is solo que or normal where junglers never gank or not well.

Kennen is an obvious pick. Hard to counter. Chop and galio are exceptionally flexible as well.

riven is supposed to counter gp. her dash gives her a shield, blocking that parley while closing the distance. almost everything in her kit allows her to beat gp. she has dashes to get over his slows. her stun gets her an AA or two. her passive allows her to deal ridiculous amounts of dmg that is more than on par's with GP's. not to mention, she has no mana issues. u should be starting armor + 5hpots

^ real level dependant GP can just as easily farm under his turret and. With parley he can farm from a distant and he has sustain through scurvy, but riven does have a upper hand but not to the degree where it is a complete lane win just because x has riven a y has gp. But you are right it certainly favors riven quite a bit.

Urgot counters almost everyone solo lane except heavy healers like garen and mundo. People use him incorrectly, but I suggest learning how to use him. One of the best champs imo. He harasses like crazy and shuts down solo top. His ult allows for a successful gank almost all of the time too.

Riven counters akali

countering depends on your jungle, your knowledge on the enemy champ and for you to effectively farm well and itemize against your enemy.

Play Irelia vs GP. Funny stuff. Just wait for him to parley then jump on him and watch him run back. You can really do this with any champions with a gap closer, just wait for him to shoot something then harass during the cooldown.