From GIZMODO: Scientists in Australia are developing a radio-controlled contraceptive implant that would control the flow of a man's sperm at the flick of a switch. The valve would be "push-fit" inside the vas deferens (duct that carries sperm from the testicles to the penis) and could be opened or closed remotely depending on the baby making needs of the user.
[Much, much more at Gizmodo]