Salamander .NET Decompiler - Web Based Demo
Reflector is cool (really, really cool), but only decompiles a method at a time. Remotesoft has a cool online demo of their Salamander .NET Decompiler that can decompile an entire assembly at a time. It's web based, so you don't even have to download or install anything - just upload your dll and browse / download your source.
Caveat: Online version only decompiles 10 methods per class. The full version look great but costs $995ish. Do not taunt Happy Fun Ball.