incoming or outgoing or damage percent would be nice to have. I keep wishing there was one, but for some reason when it comes to items with mana on them there isn't much of a selection. My character can do without a bit of health in exchange for a bit of mana.
Best I have seen are those that do mana and pip%. These are most common. Those that do school specific damage boost plus mana are very rare unless you look at clothing (hat/cloak/boots).
What is always fun to do is to go look in the bazzar.
The BriskBreeze rings all give health instead of mana from what I can find out about them. I need a ring or an athame that gives me mana as well as a couple other things to make it useful at the upper levels. I wish I could put mana on my pet so I wouldn't have a mana/equipment problem.
Hats, Robes, and Shoes are meant to have Health, Pips, Damage, Resist, and Accuracy only. Rings and Athames are designed only for Health, Mana, Incoming/Outgoing Healing, and Pip boost. Any exceptions are likely only with Crown items.