You'd have to give us a few of your preferred champions to play mid lane before we could give you tips and tricks against Leblanc.
I agree Leblanc is bullshit, cancerous, and frustrating. I don't know why Riot refuses to balance her so that she's not auto #1 pick in every game pretty much. She's even banned in quite alot of games, that should give Riot an idea of how much people dislike playing against that champion.
That said, Leblanc is not unbeatable. While there is much, much less counterplay against her in lane than any other matchups, there is still is a precious small amount IF A) Your champion has the right tools and B) Your reaction speed is fast enough / greater than the Leblanc player's. Alot of Leblanc players are overconfident and sloppy because they have the perception (somewhat justified) their champion is untouchable. You can capitalize on this mentality and these misplays. Although, you will occasionally face a Leblanc player that makes very few / no mistakes in which case the opportunities for counterplay are virtually non existent. In that case, you will just attempt to survive the lane, stall the game, and plan to win the game through teamfighting and objective control, both of which Leblanc does not really excel at if she's not very ahead.
I personally think the biggest problems with Leblanc are her W cooldown, which with a standard Leblanc build achieves 35% CDR very early in the game bringing rank 5 W down to a 6.5 sec cd (with of course the capability to return back and the capability to Mimic W for 2x the teleports). The current capabilities of her W promote very non interactive gameplay (ala pre-rework Nidalee style) in which Leblanc plays the game but never has to interact with the enemy team. The second, and less serious problem with Leblanc is her ability to do a W > Q > R > E or W > E > Q > R combo, chunking any non tank champion for massive amounts of damage at any point in the game while never risking any personal safety.