Nice add-ins for Reflector:-
(if you dont have reflector,download the same from http://www.aisto.com/roeder/dotnet).
One of the very useful add-in is the "diff" add-in. Which would point out the differences between the two versions of the same assemblies including any added/changed/deleted members/methods.
And also the "File Diassembler" where all you have to do is provide the assembly (with the dependent assemblies) you want to disassemble and it would generate the class library out of the same with all the source code.
Others are code search,Code Metrics and many more.
In order to use an add-in in the Reflector :-
a) Copy the all the binaries for the add-in in the same directory as the Reflector.exe.
b) In the reflector,View > Add-In. In the Add-ins dialog,Add the dll for the Add-in.
c) You should see the added "Add-In" under Tools menu.