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

Note: You may need to stand in front of the door and hold up when you beat Bowzer. If you don't, you may get caught in Bowzer's Trap and the game will pause forever! Some of you will get that joke, and laugh, some of you won't, and won't laugh.
Thanks to manninghere for reminding me of this little detail.

TOASTN- Freaky Mode
GITXYS- Any Block with a power up is null and void
APOZXN- Stiff Granny Walkin'
GTOZXN- Always have an odd wacker tail
PINKSO- Item fun for the whole family
GLASSS- One of the COOLEST codes ever found, ever
SAUSEE- Try and beat the game without killing any guys
KLASSS- Another doodle-doo
YLASSS- Enemy Tornado
SKELTA- Very Cool Infinite Lives
POPPYY- Anti-Mario Vision
SKEITA- Weird Black Things
GEPOZT- Bushy
OPALIN- No Box for you!
GINKOS- Mario goes to 6 flags
SAGGIE- All hail the great "Maio"
POLINI- MexicaÒo JumpiÒo
PIPSPO- Spacey Mushrooms
POPPIT- BushyX2
UNKIES- Green Block Fever
EXPETG- No world Mario
EYEKOY- One step till death
SINNNN- Watch Yourself
PINKII- Vegas Strip
KONKUS- Eternal loop
PUUZUU- Psychadellic Gusto Lounge
YUUZUU- The Best Darn Psychadellic code out there.
KOPSIT- Enemies shirk before death
PPPEEE- Cooler Level Openup
SATNAV- Even Cooler Level Openup
TOSITS- Enemito Fluctuato
TOSITI- Pile-o-crap Gumbas (and much, much more)
SOSSII- Mystical Green Block o' death
OOOSOO- Travel Through Enemies
NULUUU- Extra Cloud extraviganza
SAKOSK- A good Challenge
OZZZZI- Another Good Challenge
GIGGAS- Enemies Fall like water
(A,P,I,T)IGGAS- Odd flying enemy in the middle of the level.
KIIIIS- Flying enemies
IKGGGG- No coins a poppin'!
POTTTY- Cool SuperDeluxe Sound
KISSTS- Laced Kiss - Mario is drugged by a kiss by the princess, screwing his perception of reality. Now objects in his mirror appear closer (or farther) than they really are (ed:. Typical Ben Preston for you - see Preston Street)