I run a fairly undead-heavy game myself. Our party consists of a mon/hunter of the dead, a ranger (favored enemy undead, of course), a cleric of the sun (undead turning MACHINE), a paladin cohort, a rogue, and a sorcerer with force and fire spells.
They're pretty bad-ass, actually. Lots of damage can be dished out in a hurry to the walking dead...
I agree with the note that two clerics might be a bit much... maybe a paladin instead? Though, if one of the clerics decides to multi-class with a non-(full-)spellcasting class or a class that doesn't allow for turn undead, then you might want two. I highly recommend that at least one of the clerics not multi-class with a non-full spell progression class - they'll need the spellcasting power, particularly
restoration.
I let rangers critical their favored enemies, even if they normally couldn't be. It hasn't been an issue, I don't think he's actually managed to do it once yet. YMMV.
The party does wish it had a bard, largely because I threw a singing ghost at them (crypt chanter from Libris Mortis) and a bard could have countersonged the effect, saving them 7 total drained levels... but that's what restoration is for, right?
It's a cool campaign; they're having a good time with it. Good luck and post any particularly nasty encounters you dream up for us to yoink!
Also - here are some other threads with turn undead information and variants, including the version I use in my campaign.
http://www.enworld.org/showthread.php?t=103679
http://www.enworld.org/showthread.php?t=102223
http://www.enworld.org/showthread.php?t=98180
http://www.enworld.org/showthread.php?t=96666