1) Healer/Shaman/Mage merc's that heal/cast spells for you... Could be like a mini-portable Healer (The ones at the pits), that charge you X amount each time you use them. Of course, this would probably negate the reason of grouping with these specific classes, but there you have it.

2) Alchemist shop that makes potions on demand. Just need to go out and get the special ingredients.

3) A wizard's shop that could enchant weapons/armor.

4) A blacksmith's shop that could create custom armor/weapons.


... more to come ...