Charisma
Increases recruit rate by 4% + 2%/lvl.
supporting evidence: recruit rate of 816 Militias per turn observed with 68 barracks. This is a 20% increase compared to normal rate. 2 heroes with charisma are active both with level 3 of the ability. Therefore 2 x ( 4 + 2 x 3) = 20
My numbers from 6/29/09 do not support this formula. Bard 14 with charisma 1. 10 barracks normally provide 100 militia. Now, it's 103.