Damage vs Critical

[Closet_Skeleton]

How large can the threat range for a critical strike be? Even with Improved/Devastating critical feats, are there other ways to increase both threat and multipliers?

And what weapon would best serve this purpose of min/maxing the criticals?

In 3.0 a Weapon Master with a keen Scimitar, Rapier or Falchion and the improved critical feat could get 10-20. If you allow Weapon Master (or the overpowered Psychic Weapon Master) in 3.5 you can still get 13-20 since the only thing you're missing out is the keen property.