https://grepular.com/Abusing_HTTP_Status_Codes_to_Expose_Private_Information
A clever pseudo-hack that allows a web site to determine if I'm logged into facebook / gmail / digg / possibly other sites based on various urls which are only accessible to logged in users. Obviously smashed by noscript... :-)
http://rypple.com/
Online coaching, feedback, performance reviews, that kind of jazz, for teams or businesses based around facebook or something of that nature.
http://blog.imranghory.org/facebook-ads-the-cheapest-traffic-youll-ever
Interesting article about how effective facebook ads can be with some optimisation. Cost per clicks between a few pence and .3p per click. Food for thought. No specific advice or tips in the article.
http://fanpageengine.com/
Pimp your facebook fan page for $40 plus.
http://www.owjo.com/
Sell on facebook and other places. They handle everything for 7% plus 3% + 30c for card processing, but they'll take cards for you, no merchant account required, through elavon.
http://mooks.tv/fb_filters/
AdBlockPlus filters to block Facebook ads. :)
http://code.google.com/p/pidgin-facebookchat/
A pidgin plugin for Facebook Chat, it adds Facebook as a protocol to pidgin accounts.
http://ping.fm/
Ping.fm allows you to update a bunch of social networks in one go. Post to ping.fm and have it passed on to Twitter, Facebook, plurk, myspace, linkedin, plaxo, bebo, etc, etc.
http://sourceforge.net/projects/travelplanner/
A planned, open-source hopsitality exchange system for Facebook.
http://developers.facebook.com/
Facebook developer portal, documentation, resources, and so on.
http://www.sitepoint.com/article/developing-facebook-platform
An article from Sitepoint.com on how to develop PHP apps for Facebook