Foe Specialist( Miniatures Handbook, p. 26)
You are trained at how to damage a particular type of foe.
Sneak attack +1d6, base attack bonus +4,
Choose a type of creature from Table 3-14: Ranger Favored Enemies, page 47 of the Player's Handbook.You deal an extra 1d6 points of damage on successful sneak attacks against that type of creature. (The selected type cannot be construct, elemental, ooze, plant, or undead, since those types are not subject to critical hits.) SPECIAL: You can gain this feat multiple times. Its effects do not stack. Each time you take the feat, it applies to a new creature type from among those that remain eligible.