I'm a huge fan of Jos Buivenga's 'Museo'. It looks beautifully crafted at every weight and is easy to identify thanks to its odd semi-serifs.
That it features ligatures and multiple language support makes it all the more surprising that this font is free at most weights — and it explains why I have been seeing it everywhere, from high-street optician signs to album covers.
Despite its charm, the more I see it used the less I want to use it myself. Perhaps its popularity is a double-edged sword.