Nipple torture was mentioned. That is one of my favorites, especially when a Domme uses her nails to pinch, twist and pull. Bipolar electro nipple clamps are also a wonderful form of torture in the right hands.

One that hasn't been mentioned yet I think is irritants. Capsaicin cream can be diabolical for cbt. On the balls can be painful, but the head of the penis is the most intense, especially if it was warmed up with some whipping. It's a pain that just lasts and lasts with no escape. You know your in for the long haul with capsaicin.