Splitting from multi-ing or multi-classing, what about recreating classes by merging existing ones?
Barbarian/warrior
Cleric/druid
Mage - all robes into 1
Scout - all paths into 1
Thief/DK
Which would result, joke intended (but serious about concept), into:
Barrior
Cluid
Rainbow mage
SEAL scout
Dark Thief