I know we have ILdasm, but is there any tool out there that will let me edit .exe or .dll files without having to go through all the rigmarole of having to convert it to IL code, with resources includeded, etc etc, manually edit, then recompile again?
You could always use Reflector to disassemble whole namespaces to source code (not IL), but then you're still stuck without a direct editor, you have to copy/paste to a code file and recompile.
On the other hand, it seems like I was wrong, Reflector has an add-in Reflexil that looks like it'll do what you want.
check out this SourceForge project I guess it's what you're looking for:
Perhaps you should check out Mono.Cecil. It's a managed library for manipulating IL. You can add, remove and modify methods as you please.
Granted it's not an IDE or anything but it should be a starting point.