dotPeek is a new free .NET decompiler from JetBrains, the makers of a wide array of developer productivity tools:
You can download the beta from http://confluence.jetbrains.net/display/NETPEEK/dotPeek+Early+Access+Program
This looks like it will be a good replacement for Reflector which alas is no longer free.
You will need to do an XCOPY installation. Remember it is an Alpha release but it does promise to be an excclent FREE sucessor to Reflector.