It has been a while. Where is the rule about the CR for turning undead? As I remember, it is determined by HD. Is it 10 + HD = CR? Where is it in the rules?

Check Page 180 of the PHB (6th printing)

Ok yeah I saw it right after I posted this. It is the creature's HD that is equal to the CL. The CL then is added to 12 or 18, in this case it will always be 12. A lich has a CC of 30. Seems good.

and that just made every paladin I've ever played cry and wet themselves a little at the thought of a CL 30

don't forget situational modifiers... holy ground, curse, bless, bane, scared, coming off heroism.. I like modifying this roll. Also to roll affects each creature differently.. and just because they're a cleric does not give them instant undead ID ability... make them guess a while...

From one of my old DMs, we would add in a roleplaying modifier. If you did the epic turning dead speech, it could give big benefits to your role. Little pieces of the cleric of Thor dropping down to 1 knee at the end of the speech hitting the hammer against the floor - exploding the undead with the purest lightning / holy light!