Here is a full level hack for Super Mario Bros. that also has new graphics in it. The only difference is, even if the game's title says it's a Super Mario Bros. 1 hack, it actually contains the 32 main levels of the Japanese Super Mario Bros 2.
Super Mario Bros. (World) - NOINTRO
CRC32: 3337EC46
MD5: 811B027EAF99C2DEF7B933C5208636DE
SHA-1: EA343F4E445A9050D4B4FBAC2C77D0693B1D0922
SHA-256: F61548FDF1670CFFEFCC4F0B7BDCDD9EABA0C226E3B74F8666071496988248DE