Poise Break Points
Please note that some weapons do not obey this. E.g. the hand axe does not break 21 poise.
It has been found that certain weapon classes will stun people at very specific poise amounts. For example Ultra Greatswords, when used 2 handed, will stun anyone at 75 poise or less. So a poise of 76 will prevent you being stunlocked by a hit from an UGS. However these values will only save you from 1 hit. If you are hit again before your "poise bar" empties completely you will be stunned. The values listed are for 2 handed attacks, the values in the brackets refer to 1 handed attacks.
76 poise (51 for 1-handed resists):
All Ultra Greatswords 2h R1s
All Great Axes 2h R1s
All Great Blunt 2h R1s
53 poise (36 for 1-handed resists):
All Great Asian Swords 2h R1s
All Great Swords 2h R1s
All 1-handed Blunts 2h R1s
All 1-handed Axes 2h R1s
31 poise (21 for 1-handed resists):
All Asian Sword 2h R1s (and R2 in the case of Shotel)
All 1-handed Sword 2h R1s
All Katana 2h R1s (including Washing Pole)
All Great Scythe 2h R1/R2s
All Whip 2h R1s
All Large Spear (Partisan/Pike) 2h R1s
All Small Spear (Silver Spear/Winged Spear) 2h R1s
All Halberd/Pole 2h R1s (figured this would have been 53, but it wasn't).
8 poise (6 poise for 1-hand resists, or Fist Weapons):
All Rapier 2h R1s
All Dagger 2h R1s
All Fist Weapons R1s (although this is actually 6 since you can't 2-hand a Fist Weapon)