Facebook has been working on several new variants of their buttons and one of the interesting ones is the Want button.
The company seems to have started implementing this button in their APIs though it is not entirely functional right now.
Facebook has officially declined to comment on this button though a public launch could be just days away.
Facebook Want Button is suitable for online shopping stores where users can click this button to share that they want a particular product.
Tom Waddington has a blog post with this experimental button working partially.