From the NYT:

Steve Owens had always left birth control to his wife, who took the pill. Then Mr. Owens volunteered to test potential methods that lowered his sperm count so much that “I was not viably able to produce a child,” he said. His count rebounded weeks after stopping each method, and he fathered a daughter between research studies.

Male contraceptives are attracting growing interest from scientists. The most studied approach uses hormones such as testosterone and progestin, which send the body signals to stop producing sperm. While effective and safe for most men, they have not worked for everyone (5% do not respond to treatment). Questions about long term side effects also remain.

Scientists are testing several ways of interrupting sperm production, maturation or mobility:

Source:
http://feeds.feedburner.com/CasesBlog