Which Pokemon do you catch in Pokemon White?

If you're talking about the legendaries, the exclusive one to Pokemon White is Zekrom. You can also catch Kyurem (Giant Chasm), Cobalion (Mistralton Cave), Virizon (Pinwheel Forest), Terrakion (Victory Road), Thundurus (Stormy Route 7) and Landorus (Abundant Shrine).

Note : You must have caught Tornadus from Pokemon Black and Thundurus from Pokemon White in order to get Landorus afterwards.