CR-Based Turning (3.5e Variant Rule)

CR-Based Turning
Hit Dice on undead don't make any sense. There, I said it. Some weak undead have really high hit dice (and are thus really hard to turn), and some really strong undead have really low hit dice and are easy to turn. Stronger undead should be more difficult to turn, and weaker should be easier. So let's use the only good measure of strength in the game: Challenge Rating.

For the Turning Check, replace the amount of Hit Dice you can turn with the Challenge Rating you are capable of turning.

For Turning Damage, again, replace Hit Dice with Challenge Rating.

Undead with a Challenge Rating of at least four less than your own are destroyed instead of turned.

Turn Resistance
Turn Resistance was a spot-fix for low HD undead before. It's still important because we don't want equivalent-level liches to be turned too easily. Therefore, turn resistance adds to a creature's Challenge Rating for the purposes of turning. However, every creature that already has turn resistance has it halved.

Sun Domain
This variant rule makes turning a useful ability again, and thus supersedes other attempts at doing so such as the Sun domain. It is strongly suggested to not allow clerics to take the Sun domain (or to replace the power with something else) if you are using this variant rule.