Nonoxynol-9 (N-9) is a detergent-like chemical that has been used for over 30 years in vaginal products to prevent pregnancy. In the United States, N-9 is available in a variety of concentrations and formulations, including gels, creams, foams, suppositories, and film. In addition, N-9 is used in some vaginal and rectal lubricants and in the lubricant used in some prelubricated male latex condoms.
-from the CDC

The most popular spermicide in the world, it's also recently been implicated in causing vaginal lesions, increasing the risk of STD transmission, which seems to eliminate it from the running as an HIV preventative.