I found a deposit of Super Mario Brothers 1, 2, and 3 codes. Click here to get them (they are in text format).

ALL CODES IN WHITE WERE MADE BY EVIL_SPOCK

Altered Physics:
STALKS: All blocks are smashable, and become invisible when they're hit.
EOPOPO: At the beginning of each level, a short vine grows.
STAGXO: Faster enemies.
SONTEY: Super Slo-Mo Mario
PKKIKK: Mario can't jump
STOIKI: Jump up and you won't come down.
*AXTAK: Mario slides or warps to the left.
NININI: Mario slides to the right.
OEILET: A vertical "rain of blocks" upon hitting them.

New Worlds:
OOPSKI: World []-1: Repeating underwater world.
PIKPSG: 4-1, 1-3, freeze
OIOPOK: Underwater 4-1, 1-3, freeze
KOOPAS: Level 1: After first pipe it's all flat terrain.

Silly Mario:
TEVVEY: Vertical Multi-Mario.
EONTEY: Mario drives an invisible car.
NANYTE: Mario has the "jimmy legs".

Falling:
PKKISK Mario falls through the first layer of the floor.
EXSPTK Everyone falls thru the floor and can go thru all objects.
STAPPI Everyone falls thru the floor and can go thru all objects. (again)
STATIK Mario falls through the floor and enemies freeze.

STOIKI: Jump up and you won't come down. Actually you can come down, but only in some places, and not all the way.
STALKS: All blocks are smashable, and become invisible when their hit. Some block appear at the top of the screen. Others smash the roof blocks in the dungeons.
AXTAK: Mario slides or warps to the left. Mario can't walk fast enough to fight this. But he can move a little to the right if you jump. Could cause an aneurysm if you play it long enough.
STATIK: Mario falls through the floor and enemies freeze. If you run as soon as you start the game, you don't fall but can't move out of the starting spot.
NANYTE: Mario has the "jimmy legs". If you run long enough he'll skate instead of running like he drank 20 pots of coffe and the bathrooms at the end of the game.
OEILET: A vertical "rain of blocks" upon hitting them. There are green bolcks in random places.
STAGXO: Faster enemies. The enemys aren't always where they should be, and some platforms are farther apart.
EXSPTK: Everyone falls thru the floor and can go thru all objects. Can't get anywhere you die to fast.
PKKISK: Mario falls thru the first layer of the floor.You slide to the right, but the screen only moves when you're above ground.
PKKIKK: Mario can't jump ... this code is certain death.
SONTEY: Super Slo-Mo Mario. Certain doom again, because of the timer. but you make better time if you jump.
EONTEY: Mario drives an invisible car. He also shifts gears in mid air. And has to take his foot of the gas to throw fireballs when he's parked. He also looks big but isn't when you squat.
TEVVEY: Vertical Multi-Mario. You at random places. The screen messes up when you try to get a mushroom, which are invisible. Mostly there aren't any enemys, but what enemys there are, are actually Bowser's rear end.
NININI: Mario slides to the right. You must press right to make the screen move. If you jump you don't come down. And if you touch the side of the screen you're stuck there.
EOPOPO: At the beginning of each level, a short vine grows. Some enemys are missing. Some flags are too, when you jump on the flag pole you just fall of and don't get points. Sometimes the vine comes up behind something, so you can climb hills and look in castle windows
LAZULG- Super floaty action