Spell damage and max magicka also increase healing power of magicka cost abilities as well.

Basically if the ability costs magicka it's offensive/healing stats scale with spell damage and max magicka. If the ability costs stamina it's offensive/healing stats scale with max stamina and weapon damage.

For the times you get abilities that cost health or are free their scaling is based off the damage type and rules displayed on the ability.
So for example magic, flame, ice, and lightning scales off max magicka and spell damage.
And physical, poison, bleed, and disease damage scales off max stamina and weapon damage.

Ultimates scale off your highest offensive stat but their damage type is still effected by spell/weapon penetration and spell/weapon critical ratings so keep that in mind when picking your ultimates.