I agree with Khio Vinh that the design for ’72 was spectacular:

Every recent Olympiad must contend with what is widely considered the high watermark of design for the franchise: Otl Aicher’s seminal work for the 1972 games in Munich.

Also check out Munich72.org for an overview of the design of the Games in Munich.

But I disagree with him that the stuff done for London is crap. I love the logo.