I'm not sure if you're referring to the same Contra I'm thinking of, but there's a cheat for one of the NES Contra games that I used to use all the time...
Edit: Eh...I misunderstood the post.
Nah, this'll probably make me look like a pansy, but I never could beat SMB 1. I got to like level 7 or something, but I never could beat it. I don't think that has any codes, though.