So I had an idea for a character that joins the Mage's Guild but, disgusted with the completely single-effect spells in the inventories of spell merchants, decides to write a beginner to expert spell book with creative, and powerful, effects. It can also be two joined spells but please no spell stacking and, if your spell is quite easy or hard to cast, include a reduced or augmented spell with similar effects. I'll keep a list of the current spellbook here:

Spellbook:

Beginner:

Expert:

I'm new around here (and to this game), so I'm not sure what you mean by "no spell stacking" (but I'm probably about to violate that). I found this thread when looking for pages on people's favorite custom spells, though, and I notice nobody else has chimed in yet, so I figured I'd try to get the ball (re-)rolling.

Exhaustion
Damage Fatigue 50 points for 2 seconds on touch
Weakness to Magic 100% for 2 seconds on touch
Requires: 50 Destruction
Notes: For those who don't specialize in Illusion magic but would still like to knock foes down, this spell can be even more potent than Paralyze effects, if a bit more risky. You need to cast it multiple times in quick succession, but each time you cast it, the effect is magnified until your opponent's Fatigue reaches zero, knocking them down helplessly. It works even better when paired with some other item or effect that Drains fatigue or further increases Weakness to Magic. When I reached 75 Destruction, I raised the damage to Fatigue and added an effect to Drain Fatigue 100 points for 5 seconds; at level 30, two shots will take down a brown bear for at least 5 seconds, giving me plenty of time to practice Hand to Hand (which further damages Fatigue) or Marksmanship on a helpless foe. Recommended for use with high Speed so you can get out of the way between casts.

Heart Attack
Drain Fatigue 100 pts for 5 secs on Target
Damage Fatigue 100 pts for 5 secs on Target
Drain Health 100 pts for 5 secs on Target
Damage Health 50 pts for 5 secs on Target

Unda Equus
Water Walking for 60 seconds on Touch
This spell allows your horse to run across water instead of swimming

Here's one that works to distract and confound your enemies while you either escape or position yourself for a better strike:

Misdirection
Invisibility 30 seconds on self
Summon Flame Atronach for 30 seconds on self

I'll use these for fun while sneaking:

Flaming/Frozen/Shocking Surprise
Fire, Frost or Shock Damage 20-50 points (whatever is preferred) for 1 second on target
Drain Speed 100 points for 1 second on target

^That one does elemental damage then makes them "forget" they just got hit with a spell.

I use charm 100 points and fortify mercantile 100 points whenever buying or selling anything. I'll also use something like heal ally 20 and shield on ally 20 if I ever have an ally that I want to keep alive.

Gamebreaker
drain health 100pts 1 second on touch - cheap, low skill requirement, quick and easy way to beat just about anything you come across for a long, long time. once it begins to be inneffective, a ranged weakness to magic 100% to soften up will work. could also stick a 2 seconds of soultrap on there too if you have lots of gems you need to stuff quickly

Magebane
Absorb Speed 20-50 points on touch 15 seconds
Fortify Strength on self 20 points 15 seconds
works best with a ranged weakness to magic 100% pre-cast. basically means you can stop those pesky mages feom running away from your axe-cleaves