Nintendo - 12
Level 5 - 4
Rising Star Games - 1
Konami - 1
=66.7%
Of course I've been a little bit naughty because all of the Level 5 games I have were all published by Nintendo in Europe, so technically they should all count towards Nintendo's total, but I consider them third party.
EDIT: I also have Capcom's Phoenix Wright: Dual Destinies, not counted here as it's not retail, but given it cost fairly close to the price of a retail game it feels significant enough to mention!