Play as Luigi
Finish the game by beating Bowser in World 6. After you do that, when on the file select screen, hold down [L]+[R] while selecting a file with the [A] button. Luigi will now be your selected character.
Unlimited Use of Mushroom Houses
Clear the Star World once.
Unlimited 1ups
Same as Mario on the NES. Go to Mushroom World course 1, the place where the first star coin is. Stand on top of the stairs and wait for the noko noko. Go down to the second or third step and wait for the noko noko to reach you. Jump on it lightly (not hitting jump when you hit it) and then it should bounce off the wall and Mario will keep jumping on it, allowing you to get 3 crowns in a few minutes. Note: If you try this as Golden Mario, the Noko Noko will disappear after 25 hits.
Save File Stars
By meeting certain achievements in the game, you can get stars appended next to your save file:
Beat World 6-Castle.
Obtain every Star Coin.
Obtain all of World Star's Moon Coins.
Complete every level.
Get the highest possible number of lives.
Unlimited-Use Toad Houses
After beating every level of the game, all of the Toad Houses in the game - even if previously already used - can be reused, and reused as much as desired, allowing you to get power-ups and 1-Ups any time you need them.