The best champions outside of lane to counter Zilean include Kalista, Tristana, and Sivir. These champs are all good at countering Zilean with win rates over 57%. Even if these Zilean counter picks are not picked in your lane, it's not smart to choose him into these matchups. They will usually win against Zilean.
Yet, if the other team brings either Quinn or Skarner, you should strongly think about selecting him, as he easily destroys these champs with win rates over 55% against both ofthem.