From the Facebook blog post Updates on Your New Privacy Tools
Can I limit access to my Friend List? Many of you have mentioned that you want a way to hide your list of friends. In response to your feedback, we've removed the "View Friends" link from search results, making your Friend List less visible on the site. In addition, you can further limit the visibility of your Friend List to other people on Facebook if you want. After you've completed the transition to the new privacy settings, you'll be able to click on the pencil icon in the top-right corner of the "Friends" box on your profile. Unchecking "Show my friends on my profile" will prevent your Friend List from appearing in your profile when it is viewed by people who are logged in to Facebook. Keep in mind, however, that because Friend List is publicly available, it will be visible to people who are viewing your profile while not logged in. Again, you will only have this option once you've completed the transition to the new privacy settings. Remember, you can also limit who can find you in searches on Facebook and control whether your information can be indexed by public search engines under "Search" on the Privacy Settings page.