Veigar - Merc Treads and BV really screw up my ability to stun you and land EH. Further to that, Gankplank fully just removes scurvy and is impossible to hit. I can Q him, but he can coutner-parley me and remove scurvy to heal back up if needed. GP is veigar hard-counter IMO.
Karthas - Quick BVs on the other team are annoying (ult).
Yi - Thornmail sucks because I have to get more MR to counter. Obviously chain CC and focusing me down is rough.
Various AP burst champs (Ryze, Annie, AP Sion, LeBlanc, Lux, etc) - HP and MR are really tough to counter right now, especially on tanky dps that do good dps regardless of having full tanky gear (i.e. Nasus, Garen, etc).
Nasus - don't kite me bro
Ashe - Master Yi is my hard-counter. He can become immune to snares and my ult is the only thing I can do to keep him off me. He does WAY more dps equally fed. Only counter to this is to start teamfights earlier and hide in my team... because he WILL eat me every time. Olaf similarly is a counter to Ashe, due to his ult.