There's any number of questions about MSIL on SO but none that directly answer this.
I've been using Textpad which does have a syntax definition file for MSIL and then using ILASM in a command prompt window.
I did find a reference to ILIDE but the link is broken.
Is there an IDE or add-on / plugin to Visual Studio / Eclipse for MSIL that allows syntax highlighting, intellisense, code completion, debugging etc.?