Okay I'll take a stab at this.
COR - EXP & CP/ISP +50% (Was thinking double EXP but that's too strong)
NIN - Evasion + Enhances Dual Wield an additional 5~10%
RNG - Accuracy + medium flashy shot effect on all attacks
DRK - Attack + HP Drain on hits/Free minor souleater effect (no hp lost)
BLU - Magic Defense + reduced magic damage taken (5~10%)
WHM - MP recovered while healing + Cure Potency +10%
PUP - Pet Accuracy + Pet damage taken reduced
BRD - Spell Interrupt + Increased duration/potency of Song effects
MNK - Subtle Blow + Minor Haste (5%) buff or Martial Arts enhancement
BST - Pet Attack + Pet Haste (10~15%)
SAM - Store TP + Increased Weaponskill Damage (Overwhelm?) (20%)
SMN - Refresh + Enhances Avatar's Favor effects
THF - Increased Critical Hit Rate + Increased Critical Hit Damage
RDM - Magic Accuracy + Magic Critical hit rate
WAR - Double Attack + small chance of double damage (5~10%) on regular hits
DRG - Pet Magic Attack & Accuracy + Pet Magical Critical Hit Rate & Damage
PLD - Damage reflection + reduced damage taken (5~10%)
BLM - Magic Attack Bonus + Magic Critical Hit damage increase
DNC - Regen + enhanced Sambas effect
SCH - Conserve MP + reduced MP cost on white & black magic (10%)
I'll add my thoughts on the non job-specific rolls later.