I pocket the money and flee to a foreign country.

A good one.

I'd make a heist-planning game.

You have to form a team, case a joint, take photos, go undercover and steal blueprints, plan a route with your friends, get a getaway car, etc., and then rock the heist. It could turn into a hostage situation on the news or a shootout or a chase or all 3. Tons of options.

It'd be like an online (or local) co-op SimHeist game.

First I say "thank you", then I live my country and fly to china to spend my money! Mouahahahhahaha

I would make an FPS with an awesome new weapon: a gun that shoots blackholes. Yeah it doesn't make any sense, but it makes everything blow up and looks totally fucking sweet. You could choose between 2 supersoldiers and 8 naked chicks. I would buy 100 monkeys and 100 typewriters and give them 100 days to hammer away at a story and dialogue, which I would change as little as possible. Then I would spend 70 million on graphics and 30 million on advertising on Mountain Dew cans, and I would get GOTY and morons everywhere would say my game had "Oscar-worthy dialogue."

The other 400 million would be enough for all my other ideas in my previous posts.

Dude they already made that game

It was called Turok: Evolution

Uhhh... shit.  Well replace "black hole" with "neutron star."  Nobody will know the difference and they'll think my idea is somehow more hip and fresh.

You go around shooting Wii-fit at the masses :)

I'd probably split it up into 10 potions of 50 million and give those to some of my favorite Developers to see what they can come up with using that kind of money, among the list would be:

Atlus (would get 2 portions, one for the Persona series and one for SMT in general)
Nippon Ichi
Sega (specifically the Skies of Arcadia guys)
EA (the skate team, make them make a game without GD technical issues)
Trico
Level 5
guys who made Earthbound (I don't care that they say they're done with Mother 3, money talks.....I hope)
Shadow Hearts developers

and I'm having trouble thinking of a tenth.

1. Hire:

Hideo Kojima
Tetsuya Nomura
Shigeru Miyamoto
Hironobu Sakaguchi
Yoshinori Kitase
Nobuo Uematsu

2. JRPG in the style of FF7-FF8 on the PS3 :D

Overworks. They also made Valkyria Chronicles, I think.

I'd use my last 50 million to ressurect Working Designs in blazing glory... otherwise I'd give them to any SCE studio or Insomniac, however I don't think they're short of money =P