The two 'Legendary' Pokemon of X & Y have had their English names revealed!
Xerneas -
'This Pokémon, presumably the legendary, was announced as part of the reveal of Pokémon X & Y. In the glint of its eye is the shape of the letter X and may be based on a Chital.'
Yveltal -

'This Pokémon, presumably the legendary, was announced as part of the reveal of Pokémon X & Y. When it arms itself in flight, it looks like the letter Y and may be based on a Wyvern.'
A few more pics have been released too;
Information & Pictures from -
http://www.serebii.net/xy/