You probably don't need more than two solid front line fighters, but if you can live with 18 reputation, then Shar Teel and Kagain (both evil-aligned) are also good candidates for fighters. Shar Teel is a VERY strong human fighter with very nice dexterity, but pitifully low constitution. She can be found sharpening her blade in the Ballisk area. Kagain is a moderately strong dwarven fighter with incredible constitution (20), but relatively low dexterity. He runs a shop in the heart of Beregost. These two actually make a nice combination with Kagain acting as a tank with his regenerating hit points and Shar Teel skirting the front lines bashing heads with her raw strength. BUT, they are evil
You can also pick up Coran (good-aligned elven fighter/thief with 20 dex) in Chapter 4 if you are looking to replace Kivan at the archer spot.
--Darkman