In response to the various answers to this question at ScienceBlogs: Here’s a company that you may find interesting. They are working on a non-hormonal male contraceptive alternative. The drug target is a sperm specific protein that is apparently crucial for motility. Cool if they can make such a drug work, – but even if they can, will men use contraceptives ??

According to this site, – yes, and they even list a number of places where clinical trials are happening (although not for the spermatech drug candidate), – trials you could join presumably, if interested, for some reason or other.