Lowest I've seen was around -14. That was Jaheira with drow plate +5, a big shield and a good helm.

Only -14 ?!?!? In IWD i could get around -18 or -20. And I really hope that in BG2 I will find better items than in IWD.

And I made a mistake. My sorcerors AC is -5, but maybe Im playing wrong giving all the protecting items to my character instead of making Minsc and Keldorn be tanks. Anyway, I like to fight and get involved with my character, not sending NPCs to fight while i watch or simply cast a magic missile. I even have removed the sling +2 from my character and now he has only melee weapons. And he isnt having too much problems, using stone skin and mirror image while fighting and casting. Thats real fun !!

I can get down to -15 with Viconia and none drow armors.
These items are: Red Dragon Scale, Helm of Glory, Ring of Gaxx, Ring of Earth Control,
Cloak of the sewers, Amulet of Protection, Saving Grace.

Jahiera is a good character because of her versatility. She can wear all the armour, cast lots of good spells that other characters don't get and she fights pretty well with either the club blackblood or the +3 scimitar. I think she also has the most detailed npc. A lot of special events revolve around her and she has a lot to say. She's the most fleshed out character so to speak. I don't even give her strength enhancing items. Viconia has the strength 19 girdle so she can actually wear decent armour. By the way the best armour class in my party is -12 on Jahiera with drow plate (in chapter seven), baldurs helm and shield of harmony. The lowest in my group is -4 on Imoen just with drow chain +5.
ARMISAEL- Aerie can use shields and helms. She's got a -8 AC in my group from drow chain, helmet of defence and sentinel. Carries the mace maulers arm so has the strength to use better armour. Can remove weapon and will still get AC benifits from armour even though you're now too weak to use it. Aerie is a cleric too remember.