Some Spell ideas:
Smooth Terrain- makes all movement cost 1 movement point Tactical/strategic spell
Density- lowers combat speed of victim, cancels flying. Tactical
Quicksand- requires a dex check to leave the area, unless flying. Tactical
Nature's Blessing- increases the Con of the target. Enchantment.
Diamond Shell- makes target immune to all physical damage for 1 round. Very expensive and tactical.
Shape Weapon- improves the damage of a weapon. Caster only, and wielded weapon only, though weapons can be transferred. Encumberance increased (that was in the game if I remember) Strategic
Shape Armor- same as weapon spell, but for armor. Encumberance increased. Strategic
Alter Footing- make an opponent slip and lose his turn. Tactical.
Hallucinogenic Growth- this grows a bunch of invisible hallucinogenic Mushrooms on the ground in a forest tile. If walked through, control of the unit goes to the AI for the next turn. Strategic
Magnetic Attraction- this will pull units towards the caster each turn as their move. Target can still do other actions normally. Tactical spell with a higher level area variant.
Grow Forest- Grows a forest in a tile. Strategic one-time cost.
Wall Crash- if sieges are in the game, this spell will kill siege walls. Tactical.
Restore Walls- this spell is the reverse, it restores crashed walls. Tactical
Vibrant Sense- This spell senses life in an area, all non-flying units and cities within a radius are sensed, though not seen. Strategic.
Animal Stampede- calls an angry bunch of animals into a battle randomly within 6 squares of an enemy unit. They will attack the nearest unit, friend or foe. Tactical.