Galio, Xerath if you're really good, like numero uno good.

mordekaiser if you know how to play the matchup

ziggs is great

I run AP Sion. I can often stun her when she starts to jump at me, the shield absorbs most of her burst, and best of all, I keep her in lane so she can't roam. Sion, because of the amazing pushing with his shield, can force LeBlanc to farm against turret, which she isn't very good at. And once you cut off her burst, you can just charge her with auto attacks, which will chew her up, even despite the fact that the build is going for AP.

anyone who doesn't suck

Late game counters her just survive till then

Not much you can do early game, just try to get last hits on minions and stay away from her. You probably will die once or twice if LB is any good because of her ridiculous burst, but it won't devastate your team because even a fed LB is not good after 30 minutes.

Kassadin destroys Leblanc. His Q prevents her from pulling off combos (silence), and it does massive damage to boot. Furthermore, the silence not only stops her from detonating her sigil, but it also prevents her from effectively using her flash (if she jumps on you, a Q will prevent her from recasting to tele back, leaving her vulnerable).

Finally, kassadin's E and ult do AoE damage, which is useful when her passive triggers and you need to deal a lot of damage before she escapes.

Even a good leblanc will have a hard time against Kass, as when he gets his ult, he can just flash away when she gets too aggressive.

Buy MR and health then win. LB is easy to fight when you can see her combo coming.

Anyone who can push the lane into tower safely destroy LB early. You then force her to badly last hit under tower or waste what little mana she has on minion farming.

Also, don't be an idiot with less than 50% health and stick around bursty people. That goes for any champ that can burst.

SImple, Mordekaiser
The end.