I'd almost say just dip into a couple levels of sorcerer if your Cha is Decent
a number of first level spells were introduced in Complete Adventurer that could benefit:
Critical Strike - +1d6 damage, double threat range, +4 on crit confirmation for 1 round
Golem Strike - lets you sneak attack constructs for 1 round
Distract Assailant - One creature is flat footed for 1 round
Accelerated Movement - Move at normal speed with no penalty while using Balance, climb, Move silently...
These are just 4 examples, they can all be cast as a swift action so you can still do a full attack action after casting one.
There's more, and i know they're in Spell Compendium, I didn't mention one specificaly for Undead, though if I remember correctly there is one, much like there is for constructs.