Black cats are good luck, I believe it because they're cats.

Also, it is bad luck to harm a black cat (that's been corrupted in some places and made people think the black cats themselves were bad luck ) I would never harm a black cat, but not just because of superstition. I would never harm a cat at all.

Also, horseshoes can be good luck, or bad luck. It depends on which direction they're pointing.

One not mentioned on here, that I don't believe at all is rabbit's feet being lucky. I don't think the rabbit believes in this one...