Gran Turismo 5, the first 20 million selling GT... maybe.

[ZorroX]

http://www.polyphony.co.jp/english/list.html
Japan:
Gran Turismo 3 A-spec - 1,890
Gran Turismo 4 - 1,270
GT5 - 2M

North America:
Gran Turismo 3 - 7,140
Gran Turismo 4 - 2,980
GT5 - 7M

Europe:
Gran Turismo 3 - 5,850
Gran Turismo 4 - 6,410
GT5 - 8M

17M is ultimately best case. But with GT, you never know. Maybe online component will help sell much more, than we expect.