What three tones do you need?
Grail for heavy stuff is a good start, it has been my favourite stock module for metal, hardcore, Dream Theater etc.
If you need a nice low to mid gain crunch that cleans up well, get a Brahma, if you don't need it to clean up, and you don't mind hotrodded slightly higher gain Marshall tone, get a GTO Judge.
If you want a high gain modded Marshall type module, get a Mr Scary, or SL+ for a similar, but different slant on this tone.
If I had to live with 3 stock modules for everything, I think this would be it. Hard to decide between the Brahma and Judge, because I really love the Judge, but since it doesn't really clean up, it'd have to be the Brahma.
But hey, this is just my needs.