So... Full ranks, max starting Int, skill focus, Amulet of the Silver Tongue, a ton of skill points invested in an item familiar, and spells on top... I should be able to get all that by level 4, so from there, that should come out to (Level+3)*2+4+3+5= a +2*Level+14 modifier, with some bigger boosts as I go along... That sound about right? Should be plenty to compliment a wizard. Thanks, folks.

happy to help

You can get another +2 by being an Illumian (Races of Destiny) and choosing the correct power sigil (Naen or Krau, IIRC). The Improved Power Sigil feat increases that bonus by another +1 - and offers other benefits if you multiclass into a caster.

What's the name, and where do I find, the cleric spell that gives +10 WIS? More importantly: Is it persistable?

Are there any magic items built off a rogue's Sneak Attack ability? Say, exchange xd6 for a different ability, or does extra damage when used for a Sneak Attack?

Is there any way to use Sneak Attack against undead?

Sneak Attack Undead:
Death's Ruin - Complete Champion pg. 51 - 1/2 Sneak Attack Damage vs. Undead
Penetrating Stike - Dungeonscape pg. 13 - 1/2 Sneak Attack Damage vs. Creatures Normally Immune only when Flanking (not ranged)
Truedeath Crystal, Greater - Magic Item Compendium pg. 66 - Sneak Attack & Critical Undead

There is Owl's Insight, from Races of Faerun (I think). It's a level 5 Druid spell that grants +CL/2 Wis, not a Cleric spell.

The Madness domain can grant you up to an effective +10 Wis for the purpose of spellcasting, though it goes up to a -10 penalty for all other purposes.

I think you're thinking of Divine Agility, from SpC, which gives +10 to Dexterity, and is not persistable without Ocular Spell.

Gravestrike, SpC.

Yeah, I knew about that one, but I think Viletta might be right about the Owl's Insight. I've seen it mentioned once or twice on the CO boards. I'd forgotten about the Ocular Spell shenanigans though. Thanks!