Tool for analyzing .Net assemblies
Check out the sample report they have on the site. Really cool indeed.
http://smacchia.chez.tiscali.fr/NDepend.html
It's been developed by the same guy who has written this excellent article on iterators in C# 2.0 that not only talks about iterators but also about some cool ways to use iterators in your applications.
http://www.theserverside.net/articles/showarticle.tss?id=IteratorsWithC2