What are the different methods to detect colon cancer?

Several: Digital rectal exam, imunoassay for blood in the stool, lower GI barium enemas, colonoscopy, virtual or ct colonography, sigmoidoscopy. The best test at this time in my opinion is a colonoscopy properly performed with a proper bowel prep as it can be both diagnostic and therapeutic if the cancer is in a polyp that can be removed at the time of colonoscopy.

Multiple: Colonoscopy with biopsy is the most sensitive and specific. Other methods include flexible sigmoidoscopy, double contrast barium enema, and ct colonography (also called "virtual colonoscopy"). There are some stool tests that can serve as early detection methods, but still require one of the above tests to confirm. Talk with your doctor to find out which is the best for you.