The first ever Dota 2 tournament has been announced by VALVe using the Dota 2 blog.
With it's prize pool of 1,000,000 $USD, yes you read this right, 1,000,000$ - jaw dropping is an understatement. NVidia will also provide all the hardware for the event.
The International will be held at Gamescom in Cologne, Germany between August 17-21. This will be the first showing of the game to the wide public. 16 top teams from everywhere throughout the planet have been paid expenses and will travel to the event to show the world how Dota 2 is played in a historical inaugural tournament.
Group stage double-elimination will be the format for this and it will be broadcasted LIVE in English, German, Chinese and Russian.
Here is the list of teams participating :

GGnet

MYM

Na'Vi

CCM

LGD

TyLoo

OK.Nirvana.int

M5

MiTH-Trust

EHOME

StarsBoba

OK.Nirvana.cn

nevo

Scythe.SG

MUFC

Mineski.Infinity