Unless you are looking for a huge challenge--a cleric and sorcerer are mandatory.
The other two slots are optional--it's nice to have a character that can at master disarm early in the game----that would be a thief. You have more flexibility with the final slot--monks, knights, and paladins are all good choices.
I find Monks to be the most interesting class and thieves a close second. Late in the game these two really shine.
I'm going to do two playthroughs, evil first and then good. For my evil party I chose Monk, Cleric, Druid, Sorcerer. Since I had played a melee-heavy party in MM6 (Knight, Paladin, Archer, Cleric), I wanted to try a more magic-based party that would force me into turn-based mode a bit more often.
Obviously with that build I'll suffer some trap damage now and then, but I can live with that.
For my good playthrough I'm not sure yet what I'll do. I'm contemplating either the basic KnThClSo build or maybe Thief, Ranger, Cleric, Sorcerer for a bit more of a challenge.