Q 200! :What ways are there to automatically confirm a crit?
Unless I'm mistaken, Vorpal is a melee-only weapon property. Anyways...
I'm sure you know, but to confirm a critical hit, your confirmation roll only needs to roll high enough to hit the foe's AC. Your dice roll result doesn't need to be within your crit threat range again on the second roll.
When you're using a Vorpal weapon, your crit range doesn't matter at all. You have to roll a natural 20, period. Then you roll to confirm the critcal hit, and your crit range doesn't matter then. You don't have to roll a 20 again to confirm.
How to almost guarantee a critical hit:
The 6th level Devoted Spirit Aura of Perfect Order stance allows you to treat any d20 result as an 11. If you know you will for sure hit if you roll an 11, when you threaten a critical, just use the stance's ability to confirm the critical.
Get stuff which amps up critical confirm rolls. That way if you ever threaten a critical hit, you will almost certainly get it. The 3rd level Stone Dragon Bonecrusher maneuver gives +10 to crit confirm rolls. Combine this with Aura of Perfect Order to automatically hit and threaten a critical hit, then get a +10 on the critical confirmation. If you roll a 2 on the critical confirmation, you automatically hit and thus confirm the crit (because its like rolling a 12, and using Aura of Perfect Order to guarantee an 11 result also hit), so that's a 95% chance to hit and confirm a crit if you have >12-20 threat range and know you will hit if you roll an 11 or better.
General Critical Hit Ramblings:
More chances to threaten a Vorpal hit and/or Critical threat:
Use Multiweapon fighting. Quad wield Kurkris with a Thri-Kreen (I'm sure there are better ones out there), for 13 attacks. 13/20 chance to roll a 20 each round. Combine this with a belt of Battle or other similar things. If you can buy off LA, Time Stand still works well. If you double the number of attacks, that's a 26/20 chance to roll a 20. If you have a crazy threat range, and just want a regular critical threat, the probability of getting a critical threat goes way up.
Critical threat range cheese:
Disciple of Dispater 8 (Book of Vile Darkness) triples threat ranges with iron or steel weapons, and is explicitly mentioned to stack with Improved Critical. So that's quadruple threat range. 18-20 is 3 numbers, that becomes 12 numbers, so 9-20 crit range.