There are hundreds of different "literary devices" or techniques employed by writers of imaginative literature to enhance the effects of their work. The term literary devices usually is applied to elements of writers' style, as opposed to the actual content of the work. Another term sometimes used interchangeably with "literary devices" is "figures of speech".
Figures of speech are divided into figures of thought and figures of sound, one affecting how ideas are expressed and the other the sound patterns of the work.
On a large scale, meter and rhyme are the organizing sound devices of poetic works. Other sound devices used to enhance the effect of poems, and sometimes heightened prose as well, include rhythmic variations, alliteration (repetition of consonant sounds), and assonance (repetition of vowel sounds). In prose, isocolon (clauses of equal length) is a common sonic device.
Among the most frequently discussed figures of thought is metaphor, which illuminates one thing by an implicit comparison to something else. Another figure of thought is personification, in which an inanimate object or animal is addressed as if it were human.
For a comprehensive list of figures, you might want to visit: Silva Rhetoricae.