Epic Inspiration( Epic Level Handbook, p. 54)
Your bardic music provides greater inspiration than normally possible.
Perform 30 ranks, CHA 25, bardic music class feature,
All bonuses granted by your bardic music inspiration abilities are doubled. For example, your inspire courage ability now grants a +4 morale bonus on saving throws against charm and fear effects and a +2 morale bonus on attack and damage rolls; your inspire competence now grants a +4 competence bonus on skill checks; and your inspire greatness ability now grants +4d10 Hit Dice, a +4 competence bonus on attacks, and a +2 competence bonus on Fortitude saves.
A character can gain this feat multiple times. Its effects stack. Remember that two doublings equals a tripling, and so forth.