When the design idea is staring you in the face.
Akademie der Bildenden Künste München
Designed by BÜRO ALBA, Germany, 2008
Casa da Música
Designed by Sagmeister Inc, USA, 2007
Centre Georges Pompidou
Designed by Jean Widmer, Switzerland, 1977
Gothenburg Museum
Designer unknown
Via Gustav Karlsson (in the comments)
Habitat 67
Designer unknown
Via Jean Chouinard (in the comments)
New York Botanical Garden
Designed by Pentagram, USA, 2000
Nouveau Theatre de Montreuil
Designed by Aurelie Gasche and Delphine Cordier, France, 2007
Petronas Towers
Designer unknown
Rockefeller Center
Designed by Chermayeff & Geismar, USA, 1985
Sydney Opera House
Designer unknown
Any others you can think of?