Pikmin 3. The second installment was one of my favorite Gamecube games.
A new Star Fox game, but only if you adhere to these rules:
-Either get rid of Slippy or make him less damn annoying.
-NEVER, EVER make the player go on foot again. Fox belongs in an Arwing, plain and simple.
If you can't manage these, then just take the pretty-much-finished-yet-unreleased Star Fox 2 game for the SNES and make it available for Virtual Console.
Either rerelease the Earthbound/Mother series (all three of them) on Virtual Console or handheld, or make another installment in the series and actually market it outside Japan this time.
Better still, I'll make it easy for you. Come up with whatever concept you want, but let Retro Studios do the actual development.