The most compelling argument that nicotine does NOT cause cancer comes from the studies done on Swedish snus. Long-term (i.e. 30-year) population-level studies have found no difference in cancer rates between snus users and non-tobacco users.
While this is a slightly different administration method (capillaries in the mouth vs. capillaries in the mouth, sinuses and lungs) it does STRONGLY indicate that nicotine does not play a role.
Edit:
Here's a useful link with citations to many scientific articles:
Cancer - Swedish Match
And I was slightly mistaken. There is an increased risk of pancreatic cancer among
former smokers who switched to snus. But not of the other types of cancer.
Edit2: And, of course, Swedish snus are banned in the US. Thanks, FDA!