Eevee already has three powerful evolutions in Pokémon Go: Vaporeon, Flareon, and Jolteon.
When the second gen of creatures drops, Eevee will also be able to evolve into Espeon and Umbreon. These two new evolutions will probably cost 25 candies each.
Here's their official descriptions:
"Espeon is extremely loyal to any Trainer it considers to be worthy. It is said that this Pokémon developed its precognitive powers to protect its Trainer from harm."
"Umbreon evolved as a result of exposure to the moon’s waves. It hides silently in darkness and waits for its foes to make a move. The rings on its body glow when it leaps to attack."
If the same naming trick for Eevee's current evolutions lets you choose which second gen creatures to evolve into, you'll want to nickname your Eevee its respective trainer name from the original Pokémon show: "Sakura" or "Sayo" for Espeon and "Gary Oak" for Umbreon.