Nintendo has sent along an Eevee infographic for Pokémon X/Y, which explains the evolutionary paths available to Eevee in the upcoming game.
As you can see, the "normal"-elemental Pokémon has the capability to evolve into almost every other element, including the following:
Jolteon, Electric
Flareon, Fire
Umbreon, Dark
Leafeon, Grass
Glaceon, Ice
Espeon, Psychic
Vaporeon, Water
and finally, Sylveon, whose element has not yet been revealed.
The Eevee's previous evolutions were introduced in previous games.
All we know is that Sylveon is pink, and its bows are made of either flesh, or hair—kind of like a rhinoceros' horn is made of keratin and not bone. Makes sense, right? No, probably not. Don't try to think on it too much.
Nintendo also sent us a host of screenshots of Eevee's new Sylveon evolution, which you can see below. And be sure to read Mathew Jones' write-up on Eevee.
Pokémon X/Y is exclusive to Nintendo's new handheld device, the Nintendo 3DS, and is slated for release in October 2013. There's even a little countdown page set up by the fans, if you'd like to count down the days until you run out of free time forever.