[Will the Wierldling]

The only multi-class I go for is Halfing Fighter/Thief.
With backstab on, take the fire giant strength potion, sneak up behind someone, a specialisation in longsword and a magic lonsword... my record is 250 points with a single blow! Plus they can use the gauntlets of elven might.
I also always have two straight fighters in the party, usually a dwarf and elf. In my current party, I have a straight druid, cleric and necromancer. Druids and clerics get simular healing spells, but good clerics get generally protective spells, and druids get area of effect spells, so provides a good combo. I thinking of starting over with five fighters (three human) and dual-classing the humans into druid, cleric and necromancer when they get to level 9.
This means grand mastery of a particular weapon, and lorry loads of hit points!

Will