A prostate massage can result in a extremely intense orgasm. I haven't reached that point of my sexual habits, but there's plenty of time!
There is a hillarious scene in Road Trip (Comedy, 2000, Tom Green, Seann William Scott) where Scott plays E.L. and while donating sperm, he gets a little ass-istance from the head nurse. Suprised to feel what she is doing, he immediately screams "Stop" followed by a pleasured "ok, keep going".
That's gotta be good!