CodeCity [1]. A city represents a code base. Each class is represented as a building. The aspect of a building gives information on the corresponding class. For example: the color is the number of lines, the height is the number of methods and the width is the number of attributes.
System Complexity View and Class Blueprint [2]. Like CodeCity the color and shape represent various attributes. An added benefit compared to the codecity is that you can also show links between the code elements. For example inheritance or invocation.
NDepend [3] for .NET also has many interesting code diagrams.
[1] http://www.inf.usi.ch/phd/wettel/codecity.html