When Aeschylus's Oresteia trilogy was originally performed, it was followed up by a comedic "satyr play" entitled Proteus. This play was named after a shape-shifting sea-god whom Menelaus had to fight. This play explained where Menelaus had been while all the other action of the Oresteia trilogy was going on in Argos. (source)
Aeschylus himself appears as a character in a play by another ancient Greek playwright named Aristophanes. The title of the play? The Frogs. What's a serious dude like Aeschylus doing in a play with a title like that? Actually, Aristophanes's play is a comedy. The story takes place right after the death of Euripides, a hell-raising playwright who was born about 40 years after Aeschylus. In the play, the god Dionysus goes down to the underworld to bring Euripides back. Along the way, he passes the river Styx, which is swarming with frogs chanting "Brekekekek koax koax." At the end of the play, Euripides goes head to head with Aeschylus in an underworld poetry slam. Want to know who wins? You can read the play here to find out.
Aeschylus's Oresteia is the only surviving ancient Greek tragic trilogy. Many people think that the Oedipus plays of Sophocles (Oedipus the King, Antigone, and Oedipus at Colonus) are a trilogy, but these plays actually come from different trilogies and just happen to all connect in some way with the story of Oedipus. So, these plays by Aeschylus provide a very important window into this ancient art form. (source)
The 19th century English poet Algernon Charles Swinburne wrote an elegy for the French poet Charles Baudelaire; in it, he incorporated several motifs from Aeschylus's Libation Bearers. You can read Swinburne's poem here.
The 20th century American poet Sylvia Plath frequently refers to the Oresteia in her works, for example in her famous poem "The Colossus." (Source)