The Bill & Melinda Gates Foundation has put $100,000 behind research into using ultrasound as a temporary contraceptive for men. If successful, it would be a means to provide low-cost, non-hormonal birth control for up to six months.
The idea is that a well-placed round of ultrasound treatment would be enough to stop sperm production for six months, rendering the subject temporarily infertile. More clinical trials are needed, to achieve "maximum effect and safety" (I should hope so), but eventually the method could be a non-invasive vasectomy alternative. Even better, it could be rolled out across both developing and first-world countries.
My guess: the hardest part will be finding clinical trial volunteers. [BBC]