All codes (except as noted) work for Luigi as well as Mario.
SLXPLOVS        Infinite lives for Mario and Luigi
AEKPTZGA        1 life for Mario and Luigi after continue
AEKPTZGE        9 lives for Mario and Luigi after continue
ELKZYVEK        Power Jumps
EZKZYVEK        Super Power Jumps
EAKZYVEK        Mega Power Jumps
GZUXNGEI        Multi-Jumps
With the next code, if you let MArio or Luigi drop too long, 
you can't sky walk until you touch the ground again
SXEZSKOZ        Skywalker
OXKZELSX        Super speed running
XVUXNUEE        Turbocharged running
You must be Raccoon Mario for the next code to work
AANZKLLA        Can raise power meter while standing still so that you can fly from 
a standing start
PEUZUGAA        Start on World 2
ZEUZUGAA        Start on World 3
LEUZUGAA        Start on World 4
GEUZUGAA        Start on World 5
IEUZUGAA        Start on World 6
TEUZUGAA        Start on World 7
YEUZUGAA        Start on World 8
YPXXLVGE        Mario (not Luigi) can re-use items again and again
SZUEXNSO        Restore powers after playing an action scene (e.g. if you were "Fire 
Mario" on the map screen, then entered an action scene, died or changed to "Frog 
Mario,"you would return to the map scene as "Fire Mario")
ZEUXKGAA        Start the game as Fire Mario
LEUXKGAA        Start the game as Raccoon Mario
GEUXKGAA        Start the game as Frog Mario
IEUXKGAA        Start the game as Tanooki Mario
TEUXKGAA        Start the game as 'Sledgehammer' Mario!
If you use any of the next five codes to defeat Bowser, stand in front of the door 
and hold "Up". as soon as the door opens, you will pass through into the chamber 
where the Princess is held. If you don't do this, you may get caught in Bowser's 
time trap and the game will pause forever!
XUKXGLIE        Start and stay as Super Mario
UXKXGLIA        Start and stay as Fire Mario
NXKXGLIE        Start and stay as Raccoon Mario
OUKXGLIE        Start and stay as Frog Mario
XNKXGLIE        Start and stay as Sledgehammer Mario
SZKIKXSE        Invincibility after changing up from Super Mario (e.g. to Raccoon, Frog, etc.)
With all of the following codes, you will find that you change into Super Mario 
if you die again:
AEOSSZPA + PAOZTGAA     Change to Super Mario if you fall off screen and die
AEOSSZPA + ZAOZTGAA     Change to Fire Mario if you fall off screen and die
AEOSSZPA + LAOZTGAA     Change to Raccoon Mario if you fall off screen and die
AEOSSZPA + GAOZTGAA     Change to Frog Mario if you fall off screen and die
AEOSSZPA + IAOZTGAA     Change to Tanooki Mario if you fall off screen and die
AEOSSZPA + TAOZTGAA     Change to Sledgehammer Mario if you fall off screen and die