Thread is what it says on the tin. Now includes spell power at all levels!
Once again I invite everyone to point out errors. There is definitely stuff I've forgotten, but it's all probably quite small. All breakdowns are on this spreadsheet.
Spell Power totals before class bonuses:
Ignoring Class sources, the max spellpower for each spell type at a variety of levels is:
Class bonuses:
Not gonna do this for every level, but you can probably figure it out. For a level 20 character, this is the total.
I made some assumptions here, such as number of points spent in a tree. This is spell power per tree, not per class, again figure the build out on your own. "All" is added on to the other bonuses, i.e. Warlock ES gets 72 total Light spell power.
Warlock ES: +22 all, +50 Light
Warlock SE: +42 all
Warlock TS: +30 all
Sorcerer Savant: +30 all, +85 Acid/Fire/Cold/Elec, +10 Force. Requires stacking bonus by casting spells of appropriate type.
Wizard AM: +26 all
Wizard PM: +30 all, +31 Negative
Wizard AM: Up to +90 with Master of Knowledge, requires casting Arcane Bolt and Arcane Blast
FvS AoV: +41 all, +30 Fire/Force/Light. Requires stacking bonus by casting spells of appropriate type.
FvS WP: Assuming only taking up to fourth core, +20 Fire/Light.
Bard Swash: +20 Sonic. Requires Orb.
Bard SS: +66 all
Cleric DD: +45 all, +9 Fire, +6 Force, +18 Neg/Pos
Cleric WP: +20 Fire/Light
Cleric RS: +20 all, +81 Pos
Druid NW: +40 Pos
Druid SH: +46 all, +30 all except Force/Repair/Negative depending on season.
Artificer AT: +58 all, +60 Electric
Artificer BE: +40 all, requires charging rune arm
Racial Bonus:
Dragonborn: +30 (fire/elec/cold/acid)
Gnome: +20 all
Spell Power Feat Checklist:
Epic Destiny Feat: 20
Legendary Feat: 40 (Scion of Fire is recommended though, so unless you're using Fire, you get -10 SP in the desired element)
Maximize, Empower, Intensify: 300 (does not apply to all spells)
Empower Healing: 75 (Healing Spells only)
Past Life Sun Elf, Bladeforged, Deep Gnome: 15/30 (Acid, Light, Repair)
Spell Power Item Checklist:
All spell types:
Gear slots:
Equipment, from Cannith Crafting, Slavelord Crafting, or named items.
Implement, from Cannith Crafted, lootgen, or named weapons.
Insightful, Cannith Crafting or named items.
Quality, named items
Competence / Insightful / Quality, for Spellcraft/Heal/Repair/Perform. From Cannith Crafting or Slavelords, various other small bonuses to these skills are available. The spell power values I found also include Heroic Greensteel +6 state item.
Pots/Tomes:
Alchemical : House P vendor pots. They have up to 25 spellpower for all types except force, acid, sonic, and light; +20 potions are available for these.
Alchemical : Commendations of Valor turn in. These stack with House J pots
Tome : Mysterious Remanants turn-in. Very small bonus so probably not worth it unless you're just floating 30k remnants or something
Some spell types:
150 Enhancement
(additional) Quality
37 Exceptional : For Fire/Cold/Ele/Acid/Pos/Neg, LGS provides stacking spell powers including a massive +150 bonus that is not found anywhere else. Maybe a bug? Who knows.
Guild : All spell types except Force and Repair. Acid and Cold are bugged.
Destiny Sources of Spell Power:
Draconic tier 3: +30 Acid/Fire/Cold/Elec
Draconic tier 4: +20 Acid/Fire/Cold/Elec. Cannot be taken for same or opposing element as tier 3 bonus
Fatesinger core 6: +10 Sonic, Light, and Positive
Fatesinger tier 1: +6 Sonic
Fatesinger tier 3: +60 Sonic, +15 Force/Pos/Neg
Fatesnger tier 3: +9 Acid/Fire/Cold/Elec. Stance, cannot be toggled with others.
Fatesinger tier 4: +25 Positive. Stance, cannot be toggled with others.
Fatesinger tier 4: +6 Acid/Fire/Cold/Elec/Repair. Stance, cannot be toggled with others.
Crusader core 3: +10 Positive
Crusader tier 1: +5 all
Crusader tier 2: +30 Fire
Crusader tier 3: +20 all. Requires casting Fire/Light/Pos spells to stack bonus.
Angel tier 1: +30 Pos/Light
Angel tier 4: +30 Pos/Light. Requires casting Light/Pos spells to stack bonus.
Spell Power Boosts:
Draconic core 6: +50, 20 seconds, four minute cooldown
Wellspring of Power feat: +150, 30 seconds, three minute cooldown
Action Boost, from class: +30, 20 seconds, 30 second cooldown
Action Boost, from Human: +20, 20 seconds, 30 second cooldown
Warlock Tainted Spellcasting: +25, 20 seconds, one minute cooldown
Exalted Angel Reborn in Light gives +100 Light spell power for two minutes. Very long 10 minute cooldown though.
Xachosian Eardweller or Meridian Fragment: +25
Finding the spell multiplier for your desired class:
Take the value from the table. It already includes gear, feats, most bonuses to your skill, and a reasonable Destiny.
Then, add the spellpower you get from your class, and the stat mod to your skill (INT: Spellcraft, Repair. WIS: Healing. CHA: Perform.)
Now, add 100, and then divide by 100. That is what the base power of your spell is being multiplied by.
Example Maximum Spell Powers:
Bard Maximum Sonic Spell Power at level 30:
971 "base"
40 CHA mod (Perform)
86 Bard stuff
=1,097 -> 11.97x multiplier
Average roll of Greater Shout, using Master of Music and +3 CL/MCL from Magister (MCL of 33, may not be possible to get to CL33): 11.88 * (33d3+99) = 1,975
Sorcerer Maximum Electric Spell Power at level 30:
1,156 "base"
30 example INT mod (Spellcraft)
115 Sorcerer stuff
=1,301 -> 14.01x multiplier
Average roll of all the 1d3+3, capped at 20 (or 10, with Master of X), spells, such as Chain Lightning or Master of Fire Fireball, with Savant/Draconic MCL increases: 14.01 * (27d3+81) = 1,891
Energy Burst (no Metamagics), which gets boosted by Sorcerer Savant (iirc) and Arcane Augemention item, but not Draconic CL increase, for a max'ed Sorcerer will do an average of: 10.67 * (39d15+585) = 9,876
Cleric Maximum Heal at level 30:
1279 "base"
-300 (Heal only takes Empower Healing)
126 Radiant Servant stuff
50% Heal Scaling
=1,105 -> 6.525x multiplier
CL 18 Heal * 6.525 = 1,174.