Now that reflector is no longer a free tool (see http://www.reflector.net/2011/04/why-we-reversed-some-of-our-reflector-decision/), alternatives are gaining popularity.
2 promising alternatives are ILSpy (http://wiki.sharpdevelop.net/ILSpy.ashx), an open source initiative that initiated after the announcement by Red-Gate, and dotPeek (http://www.jetbrains.com/decompiler/) a free tool by JetBrains, the same people that brought us ReShaper.
