Some rhetorical devices are everywhere you look—metaphor and simile come to mind—and you know them when you see them. Others are less well known but just as powerful and fun to use.
Here are our top 5 rhetorical devices that aren't household names (but should be).
1. Aporia
Writers use aporia to show that there are multiple sides to a given argument. Aporia allows them to express doubt that any of these sides are correct, allowing them to give their opinions without committing themselves to one side.
Aporia, however, can be used for slightly more nefarious purposes: It can allow the writer to express a personal opinion while feigning ignorance or doubt, and it can help the writer suggest ideas to the reader without taking responsibility for those ideas him- or herself. Here's an example:

When your students see aporia in use, they should probably examine the writer's ideas very closely.
2. Chiasmus
Here's a fantastic illustration of the difference between parallelism and chiasmus:

Look how fun chiasmus is!
The last item in a sentence that uses chiasmus will have its structure reversed from the items that came before it. This adds a bit of playful panache to your writing and can surprise the reader and keep them alert.
3. Metonymy
Metonymy's an interesting case, and one that's a little tough to describe.
To use metonymy, think of an object that is closely related to another object, group, country, etc. (for example: the White House and the United States; the Kremlin and the old Soviet Union). Then, use the first object to refer to the second.
"The White House wants more of my money this year, but I'll gladly pay higher taxes if it goes to education."
In the above sentence, "The White House" does not refer to the building (a building, of course, would have no use for your money) but instead the United States as a whole.
Here are a couple more examples:

4. Anaphora/Epistrophe/Symploce
Okay, this one's cheating a bit, but we had to get these three in — and they're closely related.
When you use anaphora, you repeat a word or phrase at the beginning of successive clauses or sentences.
When you use epistrophe, you repeat the same word or phrase at the end of successive clauses or sentences.
When you use symploce, you repeat the same words or phrases at both the beginning and end of successive clauses or sentences.
Here's another illustration:

5. Zeugma
When you use the one word or phrase to join two seemingly unrelated ideas, you're using zeugma.
This is our #1 for a couple of reasons. First, it's really cool. When used well, zeugma is one of the most shocking and delightful rhetorical devices there is.
Second, zeugma is tough to use. Finding the right word or phrase to join your two ideas can be challenging. Here are a couple examples:

If you want to challenge your students to use more creativity in their writing, ask them to come up with a few examples of zeugma.
When used sparingly, zeugma is a great tool for grabbing attention. It's powerful and clever, and it definitely deserves the #1 spot.
All examples taken from the Prestwick House Rhetorical Devices PowerPoint for the Classroom PowerPresentation.