Who's work should I read that would have the most influence on a high school student, besides aristotle?
OMG. you're only in high school holiday? It is always nice to start with the Greeks. Read Plato's original work, especially the early works for an introduction to Socrates. Meno - for epistemology. The Republic for ethics and political philosophy. Apologia for an in depth study on the nature of Truth and philosophers.
If you like you may want to look into St. Thomas Aquinas' Five ways in prooving God's existence in his Summa Theologica.
It is also important to look into William of Ocham's Razor.
Rene Descartes Meditation on First Philosophy is a required reading if you want to go further in Modern and Contemporary Philosophy.
Then look into Berkeley, Locke and Hume.
Immanuel Kant is a diificult reading, but never neglects kant's Categorical Imperative.
There are other influential philosophers but what i listed I think is enough for now.