I’ve been looking for a while and finding well, nothing.
I’m trying to find a (not necessarily unity specific) advanced visual shader editor, if not unity specific then engine agnostic and able to generate CG.
The only ones i’ve found are mental mill (no longer sold) and ShaderFX (no longer sold either!) all the rest is directly part of 3D packages which i do not own and definately wouldn’t purchase “just” for the shader editor at 3K$ a pop.
Anything i missed?
Have you tried out Strumpy? It is open source now, but it is a viable option 
I don’t think it’s quite in the same league as those visual editors, it’s node based yes, but much lower level last i checked it out and unity only, i’m more looking at high level shader design and combines with real time preview, not game specific low level tuned shader design. (basically i’m looking for a prototyping tool )
Funny you are mentioning this now… I was looking for Mental Mill also… sad that it is gone 
I know this thread is a couple months old, but mental Mill 1.2 Standard edition was re-released by nVidia in January.
http://forum.nvidia-arc.com/showthread.php?12284-mental-mill-1-2-release-and-download
thanks so much for posting this! had lost any hope of finding this tool after looking late last year!
I have made some research, and it looks as though mentall mill is not beeing developed any further, at least that´s what I heard from a very reliable source