Liches are obviously tough to beat, even by themselves. I noticed a particular pattern they use before using the dreaded "time-stop" spell--they cast "stone-skin" and some sort of protective magic bubble (I forget the terminology, so forgive me). I was wondering--what spell would remove these combat protections. I've tried "breach," "secret word," and "pierce magic," and they seem to work only part of the time.

Hey, how about that "Wail of the Banshee" spell? Nasty, nasty, nasty.

Make sure you have a spell trigger for spell turning, spell deflection and spell trap. Activate it just before the lich appears. Then use abi-dalzim to kill off about 30hp. Abi dalzim should prevent his time-stop from being casted (spell failure) and hopefully you can cast a few more to kill him off quickly. The spell turning and deflection is to protect you from further damage whilst you cast, also prismatic spray works as well.

Don't worry about his chain contingencies and other crap because from my experience it protects him from none of these attacks.

Lich casts Stoneskin and Spell Deflection/Spell Trap and also Mislead. If he casts Mislead you won't be able to target him with Breach etc. As Archmagi said have some kind of spell deflection (depending on your level) ready. Cast True Seeing to get rid of his Mislead, then you can use Breach to strip away his Stoneskin and the spell removal stuff should work against his spell protections. A really good offensive weapon to use against liches is false dawn and insect plague, he won't be able to cast anything. Power word Stun is a very underrated spell, it's almost like a time stop where your entire party can move.

BTW He's usually dead by the time his chain contingency goes off.