A: Well, there's always the foreskin piercing - something only uncircumcised men can have. Information about that piercing is here: http://tattoo.about.com/cs/beginners/a/blforeskin.htm
Also, most piercings of the glans (head) of the penis can also be pierced, such as an apadravya or prince albert. The foreskin simply needs to be rolled back first and it is important to keep the area extra clean during healing time. More information about genital piercings can be found at http://tattoo.about.com/cs/beginners/a/blmalegenp.htm.
Depending on your particular anatomy, certain piercings may be more favorable than others. It's best for you to visit your piercer and have a consultation about your options.