One of the more intriguing ideas I've heard lately is for an alternative version of the Monster Manual with better monsters.
I think this is a rather interesting idea, and could even see myself ponying up for an entirely new MM, even if it contained the exact same entries.  Honestly, I don't really need more monsters, I just want the ones I've got to have more variety.
The main thing I would want is more special abilities/actions for every monster.  
Even better, if each monster had some variability.  I think the idea of "Feats for Monsters" (c.f. another thread) raises an interesting idea.  What if many/most/all of the monsters had a list of Feats, from which the DM was supposed to pick one?  That way even players who had read the MM cover to cover wouldn't be 100% sure of what they were facing.  (That is, for the kind of DM who describes his monsters by their name in the MM.)
I could also imagine monsters with multiple entries to cover a range of CRs (sort of like Dragons).  It's always bugged me that all...fill in the blank...are exactly the same power.  (My dream digital tool is a Monster Manual where you adjust a slider, CR 1 to 20, and the monster scales appropriately.)  
What else could be in the Badass Monster Manual?
And what would be the best name for such a tome?