One of my favorite books is Bertrand Meyer's Object Oriented Software Construction
The book explores object oriented programming using the Eiffel language and one of the things that I always loved about Eiffel was the defensive programming techniques that it teaches and the strong focus on contracts and preconditions (a technique that is used extensively in Gnome).
Until very recently I had not noticed it, but the Eiffel compiler and the Eiffel suite of libraries and even the development IDE (EiffelStudio) were open sourced (Emmanuel mentions this to me during the Lang.Net conference and I do not remember any big news about it).
They have just launched a community site Eiffel Room.
There are a bunch of Flash-based presentations on Eiffels here.
In this presentation you can see a demo of the IDE. In particular see the "System Metrics" section.