Here are all of the ways in X & Y (which I assume you are talking about) besides breeding, There are more ways in B/W and B2/W2, as seen here.
Friend Safari - Pokémon in the Friend Safari have a small chance of having their Hidden Abilities. This chance is unknown.
Horde Encounters- Horde Pokémon have a chance to have their Hidden Ability. It is still not known, as seen here.
Here's a run-down on breeding:
If you breed a Female Pokémon with a Hidden Ability with another Pokémon, they have a chance of giving that Ability to each of their children. This chance is 60%.
With X&Y, Male/Genderless Pokémon also have the chance to pass down a Hidden Ability to their children (Light Metal Metagross! Woo hoo :(. I guess Analytic Porygon-Z is fine though), but only when bred with a Ditto and if the father (the male or genderless Pokemon) has the Hidden Ability. This chance is unknown.
Source: Above links