My first two toons to 60 in classic were lock/lock. Then I did mage/priest (very painful in comparison). After classic I generally leveled up pairs where one of them was a lock: lock/druid, lock/priest, etc.

If you want a pocket healer for your warrior, war/shm is good.

If you're thinking about a group of 3 with tank/healer/dps you might as well go tank/healer/3xDPS. Other than the money and some setup time, it's no more difficult to run and then you can do dungeons. My current 5-man group is paladin(tank), druid(healer), mage, lock, hunter. It's actually easier than my first group of war/priest/3xmage.