1. My hardest battle was when my party tackled the Horrors and Invisible Stalkers in the mage's house (NW portion of BG city) - the same mage who gave the Balduran quest.
2. Picking up Coran - he was a killer back-stabber when equipped with the Boots of Speed!
3. Minsc - need I repeat the sentiments of countless others?
4. Venturing into a Web spell with Spider's Bane in hand, and later switching to to composite long bow while still within the area of effect.