There is a tremendous amount of agreement across all denominations that certain actions are always sinful: murder, adultery, idolatry, blasphemy, etc.
There are also a number of actions that are viewed differently by the various Christian traditions. (This list is nowhere near complete...)
- Baptist denominations generally believe it is wrong to drink alcohol except for medicinal purposes.
- The Roman Catholic church teaches that birth control is wrong.
- I have heard some individual pastors teach that "rock music" is always sinful.
- There's a song titled If Your Hair’s Too Long, There’s Sin in Your Heart. While it's intended to be comedy, all good comedy is funny because it's based in truth (not that I personally think long hair is a sin, but I have known people who did).
- Seventh Day Adventist hold church services on Saturday instead of Sunday.
- Many Church of Christ churches do not use musical instruments.
I'm not sure all of those things are considered "sin" by the groups that avoid them, but if you look at the differences between traditions, you'll be able to find more areas where they differ on their understanding of what is considered sinful.