AsmSpy

A simple command line tool to view assembly references.

How it works:
Simply run AsmSpy giving it a path to your bin directory (the folder where your project's assemblies live).

    AsmSpy D:\Source\sutekishop\Suteki.Shop\Suteki.Shop\bin

It will output a list of all conflicting assembly references. That is where different assemblies in your bin folder reference different versions of the same assembly.

To see a list of all assemblies and all references, just add the 'all' flag:

    AsmSpy D:\Source\sutekishop\Suteki.Shop\Suteki.Shop\bin all

The output looks something like this:

....
Reference: System.Runtime.Serialization
	3.0.0.0 by Microsoft.ServiceModel.Samples.XmlRpc
	3.0.0.0 by Microsoft.Web.Mvc
	4.0.0.0 by Suteki.Shop
Reference: System.Web.Mvc
	2.0.0.0 by Microsoft.Web.Mvc
	3.0.0.0 by MvcContrib
	3.0.0.0 by MvcContrib.FluentHtml
	3.0.0.0 by Suteki.Common
	2.0.0.0 by Suteki.Common
	3.0.0.0 by Suteki.Shop
	2.0.0.0 by Suteki.Shop
Reference: System.ServiceModel.Web
	3.5.0.0 by Microsoft.Web.Mvc
Reference: System.Web.Abstractions
	3.5.0.0 by Microsoft.Web.Mvc
....

You can see that System.Web.Mvc is referenced by 7 assemblies in my bin folder. Some reference 
version 2.0.0.0 and some version 3.0.0.0. I can now resolve any conflicts.