[SixOfSpades]

I think Lemernis ran a party with 6 Specialist Mages once, but he didn't finish the game. I tried soloing a Half-Elven Conjurer with 96 points, but ground to a halt when I couldn't kill the Flesh Golems when I was low-level. (You can bypass their Magic Resistance with Darts of Wounding, and the Fleshies have poor Save vs. Death. This didn't work for me, however, because of my pititful THAC0.)

I'd suggest a Thief/Mage, Elven if possible. Not only is it versatile and powerful, but it's a lot of fun when you're a good player.

Alternative idea for a party:
Paladin (Ajantis)
Cleric (Branwen)
Druid (Jaheira)
Mage (Imoen or Xzar)
Bard (Garrick)
Mage/Theif (Imoen or PC)
Each member is one of the 5 classes who can use spells (or spell-like abilities) in BG1. The difficulty will be your Thief skills, but the good side is this party isn't too much of a stretch from the standard Tank setup.