Fighter/theive is probably the best way to solo the game; that what multi-classing is really for. But fighter/mages can also do pretty well if you don't bother with any, or atleast few (magic missle, fireball), offensive spells. If you only cast defensive spells you can compensate for not using any armor *SPOILER*If you kill Drizzt you can wear his armor and still cast spells. Blur and other spells like that can also make you almost impossible to hit.
