Given the roaring success of the very long lvl 10-15 spells list, I thought i'd try and get another such going.
So, please post your interesting lvl 20 to lvl 30 spells here.
I'm looking for interesting spells, especially crafty and cunning uses of the spell guidelines. Really not interested in your slightly-more-powerful PoF spell. Show me something cool.
I shall contribute some of my own as soon as i get to my notes.
Or, one could compile such spells and submit them to the Open Call...
Subtle strike of Divine Fury
ReAu20
R: Sight, D: mom, T: Ind
Summons a lightningstrike from an existing thundercloud you can see, that will strike where you direct doing +35 damage.
Far more subtle than most combat spells, this also has the advantage of being very powerful for it's magnitude. Combine with a storm making spell to start the fun;)
Base 5, Sight +3.
I'm not sure I'd allow that spell as written. It's too powerful as a combat spell, I think. So... if someone tried to make a spell like that, I'd probably limit him to...
causing a storm cloud to release lightning (you could try to target it, but it would have a massive difficulty for the finesse roll, given the wide area the lightning could potentially hit),
This one uses the 'control a severe weather phenomenon' guideline (base 4, so a magnitude easier) to control a thunderstorm. Concentration duration could still make this pretty devastating to an army or town (provided, in the latter case, that you can handle the casting total penalty for targeting something within the Dominion.)
or...
direct a bolt of existing lightning, which would require at the least fast-casting mastery, and up to the storyguide if it's even possible then. This wouldn't require a finesse roll, though.
This one uses the 'control a very severe weather phenomenon' guideline (base 5, the one you seem to be using) to control a lightning bolt.
EDIT:
It would be very cool to see two Auram magi working together to do this. One summoning the lightning bolts from the storm, the other directing them at targets.
OK, a couple from me
Tenebrous’ Brief Touch of the Heavens
ReCo30
This is a favourite attack spell of Tenebrous’ and allows him to teleport his foe directly up in the air 500 paces. At this point he generally steps back and watches gravity take over. Falling from 500 paces is usually fatal (+30 damage, +25 if landing on something soft, +50 if landing on something hard). The “sky diver†has approximately 8 seconds to do something daring to save himself. Most mages, assuming they maintain a level head should be able to manage a spell to halt their descent and so Tenebrous typically uses this on a rival mages shield grogs, effectively forcing the magus to move or be crushed under these fleshy “Dumb bombsâ€.
(Base 20, +2 voice)
Not sure about the damage here, by the book it should be 250, 125 and 500 but that seems a little silly really.
Lunar Curse of the Walking Dead
ReCo30 (Me)
This terrible spell animates all the dead bodies within the ring at the time of casting. These corpses remain animated for a month before dropping down dead again. They are very stupid and tend to follow verbal orders from their creator literally and display very little imagination. Tenebrous typically uses this spell to create and maintain an undead workforce for the covenant's tin mine. Every month before the new moon he orders all the undead to one location, the day after the new moon, he draws a circle around that location and re-animates them.
(Base 10, +1 touch, +3 moon, +0 circle)
I fully confess this is a crafty attempt to have lots of zombies walking around under my magus' control without using vis. I quite like it.
Dimming the Daylight
PeIg25
With this spell Tenebrous can greatly lower the light in an area 100 feet across. Within this area visibility shrinks to within arms reach, bright lights (such as torches) become dim but can b seen from about 15 feet away. Even in bright sun light this effect turns everything in its area to twilight conditions.
(Base 2, +2 voice, +1 diameter, + 4 size)
I like this spell as a great means to either terrify ones foes or to beat a hasty retreat. I also love the imagery of a large room full of enemies going pitch black and only screams being heard from inside until finally the spell ends and the room is full of corpses with a single magus still standing. Very Hollywood.
Heh. I wonder how many botch dice you get on that roll. 
Anyway, here's a couple submissions from me:
Hammer of Bone-Crushing Might
This spell is an unusual combination of two spells, using the guideline that 'combining' two spells adds one magnitude if the weaker effect is below sixth magnitude.
Creating the Hammer:
Creo Terram 25 (base 5, +1 touch, +1 diameter, +2 group)
Throwing the Hammer:
Rego Terram 20 (base 15, +1 touch, +0 momentary, +0 individual)
The Final Effect:
Hammer of Bonecrushing Might
Creo(Rego) Terram 30 (R: touch, D: diameter, T: group)
This spell creates a black iron ball in the caster's outstretched hand, then immediately propels it away from his palm as if fired from a catapult. Trailing behind the ball until it reaches its maximum range, a chain of the same metal appears link by link, attached to it.
Hitting with the spell requires both penetration and a successful targeting roll (with a range increment of 20 paces), and deals +15 damage on impact.
And another effect that magi would often learn to accompany that one:
Boneshattering Flail
Perdo(Rego) 20 Terram (base 5, +1 touch, +0 momentary, +1 part, +1 rego)
This spell, based on Obliteration of the Metallic Barrier, is typically cast on the chain of the Hammer of Bonecrushing Might, using target: part to actually affect the ball, which explodes in a hail of shrapnel, spreading a good ten paces in each direction and dealing +10 damage to everyone in the radius of the effect.
In my games, these two spells can be found bound in a book which also contains a tractatus on spell mastery for each spell and a tractatus on Terram. The first of the two spells was submitted to one of the House Bonisagus folios.
A possible variant of the first spell, which would be level 35 to encompass a longer duration than 'diameter', might create a grappling hook instead of an iron ball.
I remind you all that there are six lovely level 10-15 spell combos aching to be filled over at the previous thread.
They've been empty for over a year. Can't you help them?
Tunnel of Merinita
ReVi 30
R AC, D mom, T Ind.
A spell cast simultaneously with tunnel of Merinita has its range determined not between the caster and the target but between the caster's familiar and the target. The familiar chooses The specifics of the targeting rather than the caster (and may, in some cases, need to make a finesse roll for targeting). the caster must make am Int + concentration roll against an ease factor of 9 to cast this spell successfully with another. Tunnel of Merinita can not carry a spell of higher than level 15.
base 10 +4 range Arcane connection.
Hey, I really like this one! Cool idea 
Talk about incinerating touches or boulders falling from the sky! (yes, my familiar used to be a small raptor)
Cheers,
Xavi
Oo. Eye range ReMe spell, cat familiar. "Come here and pet me, puny human". Talk about inconspicuous distraction... 
Wizard's Window
Perdo Imaginem 20 (base 4, +1 touch, +2 ring, +1 part)
This spell destroys the ability of part of a wall or surface (described by a magic circle) to affect sight for as long as the circle remains unbroken. The image tends to look a little odd, like a painting with depth, as the species travel through the surface but light itself does not, so that bright light from outside doesn't light up the image to someone looking at it from inside, for example, while light inside does light up the image even if it's actually dark outside. A version of this spell could be created, at level 25 with a Rego and Ignem requisite, to allow light to pass through the surface.
A question, is there some problem investing this spell as a power in the familiar bond?
I would need only a Touch range instead of an AC.