Of all the spells in the game, I always thought Reincarnation was one of the best (and least used).
Maybe it is being saved for Druids (I don't know) - and obviously it would be somewhat situational - but you could set it so the spell duration lasted until the player requested a heal from the tavern cleric or logged off.
That would throw MANY of us a fun bone (imagine all of the wild dogs running around Stormreach). If it was limited to or restricted to simple creatures, there would be no game breaking components (no one would become an Orthon).
Obviously there are many other things people could do with their characters - even the Druid transformation types could be 'pre' tested by allowing reincarnation (or Polymorph).
The other spell is Summon Familiar (spell / ability).
This one is SO simple to implement. Give the players a familiar that becomes permanently bound to their trinket slot until it is killed (or dispelled). Have a dispelled familiar impose some sort of long term death penalty (10 min per level of the spell / familiar or so), and a killed familiar an even more severe penalty (20 min per level) so as to prevent abuse of the Voice of the Master and other trinket items.
After all, one does not just 'swap out' their spouse, children, or favorite pet (not comparing children or spouses to favorite pets - but if the shoe fits...).