Facebook - A social networking website that got made into a movie in 2010.
Faves - A bookmarking/news site.
FeedBurner - A google owned blog to e-mail / rss service.
Feedjit - A free or paid option tool for monitoring blogs/websites via a widget.
FeedM8 - Convert web blogs into phone friendly blogs.
Flickr - A yahoo owned photo sharing website.
Floating Action Button - A tool for creating floating windows on blogs/websites.
Forum Know How - A Internet Marketer's forum - advice and chat with REAL web marketer's with a proven track record, no BS. $10 a year membership fee.
FourSquare - A location based social networking service.
Free Monthly Websites - Free websites monthly, club run by Dave Nicholson and John Thornhill - UK web marketers.
FriendFeed - Profile aggregation and conversation platform owned by facebook.
Friendsite - A social network.
Friendster - Was popular before Facebook took off.
Fun Guppy - A free or paid classified portal/advertising website. Link Submitter, Ad Blaster, Link Swarm
Funny - If something can make your laugh, it can change your thinking...
Furl - It was a bookmarking site, now redirects to Diigo.