Facebook Breakup Notifier: this is 21st century romance
Speaking on behalf of romantics everywhere, the service is depressingly simple to use. Seriously, it's a 3-step process -- and to be honest, it kind of takes all of the effort (read: romance) out of Facebook-stalking your crushes. Anyone who has successfully chatted up a boy or girl online will know that timing is by far the most important factor, and with Breakup Notifier in your arsenal, rebound hook-ups are an easy, foregone conclusion.
Breakup Notifier is free for now -- but considering Facebook historically bans 'who defriended me?' apps, it might not be around long enough to make the developer any money. Better strike while the iron's hot, eh?