Script Summary: Log out of Facebook Chat and still see who is online.
You can log out of Facebook Chat and still see who is online. Updates every 60 seconds. You can Show or Hide each of the options using Greasemonkey's User Script Commands
Display online friends on top of Facebook Chat
Click the title to show/hide the list and click x to remove altogether.
Want to know who has been online?
Open up a new tab in Firefox, load up about:config and filter for "Facebook Online Logger". You will see a list of your friends names, the time they came online, and the last time they were seen.
DISCLAIMER: This may violate Facebook's Terms of Service. Responsibility for any violations is held by the user, not this author.