Since RedGate's .net reflector is a commercial tool now (which is not free), there has been a need for a free tool for decompiling .net assembly. Well, JetBrain has impressed yet again with its own product for disassembling. Although not officially released yet, the current version of the build was pushed on December 29, 2011. This product is named as dotPeek. This is what they are saying:
dotPeek is a new free .NET decompiler from JetBrains, the makers of a wide array of developer productivity tools.
Browsing namespace hierarchies
All you need to do is drag and drop the assembly in the tool and just browse through the namespace hierarchies to find the required type.
Browsing Type Hierarchies
Type hierarchies can also be navigated using the same assembly explorer. You can not only see the decompiled version of the type but also its inheritors and base classes. It also displays the interfaces that the type is implementing.
The type hierarchies can also be viewed in Assembly explorer.
Find Usage of a symbol
We can find the usage of a symbol like we do in visual studio. But definitely it would be able to get the usages in just the assembly loaded.
This can be downloaded from here: