Well, I personally like the Diff and FileDisassembler, another add-in which is not hosted at the CodePlex. Diff is a tool that act like Windiff to your file compare, but it's used for assembly compare; while the FileDisassembler allows you to reverse-engineer the assembly to the source file, in case you loss your source code (and of course, if you wanna see how people code :-D), althought it might not 100% identical to the original code. (But hey, what you can ask for, since it is free!)
(Image from Reflector.FileDisassembler)
Must-have and go get it!