Homer brings the gods into The Iliad as well, which tells the story of the mythic Trojan War. Most of the gods of Olympus take sides in the human war: Hera, Athena, and Poseidon are rooting for the Greeks, while Aphrodite, Ares, and Apollo fighting for the Trojans. Be sure to check out Book 7 and Book 16 for the detail on Apollo.
The Oresteia is a trilogy of tragic plays (Agamemnon, Libation Bearers, and Eumenides) by the ancient Greek playwright Aeschylus. These plays are about how Orestes and his sister Electra take revenge on their mother for killing their father. As in any good Greek tragedy, the characters call on the gods for help, and Apollo and Athena become pretty involved in the third play.
Euripides's play about Medea, the wife of the hero Jason, uses Apollo and the other sun god, Helios, as symbols. Learn all of the details here.
In Sophocles' famous play about fate, Apollo's oracle at Delphi pops up pretty often.
In Sophocles' tragic play, Apollo commands Orestes, Electra's brother, to kill their mother.
In the Roman poet Virgil's epic poem, Apollo's various oracles, especially Sibyl, provide the hero Aeneas with prophecies.
The Roman poet Ovid collected all kinds of wild stories about the gods in The Metamorphoses. Here you'll find myths about Apollo, including those about his defeat of Python, his love for Daphne, and his music contest against Pan. Be sure to check out Book 1 and Book 11.
In this Shakespeare play, the characters doubt Apollo's Oracle, but then pray to him for forgiveness in Act 3, Scene 2.
Check out this poem to Apollo, the god of poetry, written by the Romantic poet Percy Bysshe Shelley (that would be the Frankenstein lady, Mary Shelley's, husband).
In this Star Trek episode, Apollo appears on the starship Enterprise: "A powerful being claiming to be the Greek god Apollo appears and demands that the crew of the Enterprise disembark onto his planet to worship him."
Percy Jackson has run-ins with all of the gods of Olympus, including Apollo. We don't meet him in the first book, The Lightning Thief, but we meet many of his mortal children (they fill a whole cabin at Camp Half-Blood). His first appearance is in the third book, The Titans Curse.