My BF read about the Full-Body Dual Orgasm Technique in a book. I love it, the woman enjoys simultaneous clitoral and G-Spot orgasms. The short version:
There should be some foreplay to get the woman excited. The man then gives her oral stimulation to the clitoris. He waits until she is highly aroused then he teases her vagina with his finger before inserting it while continuing the clitoral oral stimulation.
While continuing the oral, he stimulates the woman's G-spot with his finger. (To stimulate the G-Spot the man gently and slowly rubs his finger on the spongie ridge of flesh inside the vagina along its roof).
When orgasm is acheived, it fills your entire body. It's much more intense than a clitoral orgams.
The book of sexual techniques he found it in was 'Recipes for Better Sex.'