Mass Effect 2 commercial during NFC championship game Saints-Vikings was the best video game commercial ever. Big opening week but weak legs.
The first LittleBigPlanet sold 4 million on word of mouth with non-existent advertisements. The 2nd game has massive potential. A primetime commercial that shows off the graphics and power of LBP2 would be awesome of its sale.
DC Universe (which I think it's a great game) has lots of untapped potential with all the DC fanboys out there.