Which characters in Acts 1-3 of Shakespeare's Julius Caesar use rhetoric?

Rhetoric is the art of persuasion and Julius Caesar abounds with persuasive speeches. Shakespeare scholar David Bevington calls the play a "study in civil conflict," and persuasion is a key part of this. If Hamlet is constantly talking to himself and bemoaning his own fate, the characters in Julius Caesar seem forever to be addressing the crowd—or trying to persuade one another.

An early example of rhetoric emerges in Act I. Despite the warning of Cicero, himself a master rhetorician, that "Man may construe things after their fashion," Casca nevertheless falls for Cassius's rhetoric when Cassius interprets the recent violent storm as a "warning" against a "monstrous" occurrence: the senate's plan to make Caesar king the next day. Cassius speaks eloquently of this as "tyranny" and states that the Romans are "sheep" to allow Caesar to be crowned. Casca is stirred up and states at the end of this speech  that he will stand with Cassius and go as far "as who goes farthest."

In Act III, Caesar uses rhetoric when Brutus and Cassius ask him to pardon Cimber. Caesar depicts himself as not just a person, but as an immovable force of nature, like a star:

But I am constant as the northern star,

Of whose true-fixed and resting quality

There is no fellow in the firmament.

After Casca and the others, including Brutus, stab Caesar to death, Brutus uses rhetoric to persuade the crowd he and his cohort were loyal Romans in betraying their friend. His exhortation "friends, Romans, countryman" is one of the more famous openings of a dramatic speech. He goes on to spin his murder of Caesar as a noble sacrifice: he states that he loved Caesar, but he loved Rome more. He said he stabbed Caesar to win the freedom of his fellow citizens and for love of his country, and that he in fact weeps out of love of Caesar and honors him for his courage. Brutus might be covered in blood, but he paints himself as lily white and pure. 

Perhaps the most famous example of rhetoric, however, is Mark Antony's speech following Brutus's, in which he undercuts Brutus's protests of honor with sarcasm, repeating over and over, "Brutus is an honorable man" in a way which reveals Brutus to be anything but honorable in his killing of Caesar.

In this play, Shakespeare shows the power of rhetoric, or "spinning" a situation, to win approval or persuade, especially in the public arena.