Aristophanes, The Clouds 

Aristophanes was a contemporary of Socrates, and in this play from about 423 BCE (about 25 years before the events described in The Apology), he offers a sharp parody of Socrates.

Plato, Euthyphro

A dialogue written around 380 BCE (about 20 after The Apology), in which Socrates' main accuser Meletus is spoken of harshly.

Plato, Phaedo

Late work by Plato written around 360 BCE that describes Socrates' early views regarding death.