I happened to see some pictures (via Archdaily) from various pavilions’ construction yesterday for Shanghai Expo 2010 and it made me recall when World Expos were actually synonym with architectural experiments and innovation.
In 1958, Le Corbusier and Xenakis designed the Philips Pavilion for Brussels’ Expo
In 1967, Montreal’s Expo hosts various innovative buildings designed by Frei Otto (German Pavilion), Moshe Safdie (Habitat67) and Buckminster Fuller (Biosphere).
In 1970, Kisho Kurokawa designed three buildings for Osaka’s Expo as metabolist manifestos. 

Today, the French pavilion for Shanghai 2010 is pretty representative of the global quality of architecture (as far as the Expo is concerned but maybe also in general): it is drab, conventional and thinks it talks about sustainability because some plants grow (have been plugged) on it… I talk about the French one, but the others are not so interesting either…Heatherwick’s British pavilion might be the only one interesting questioning the notion of archive by hosting a giant seed bank.