Mage Slayer( Miniatures Handbook, p. 27)
You have studied the ways and weaknesses of spellcasters and can time your attacks and defenses against them expertly.
Spellcraft 2 ranks, base attack bonus +3,
You gain a +1 bonus on all Will saving throws. Spellcasters you threaten may not cast defensively. (They automatically fail Concentration checks to do so.)