I think that these rings have some merit. Here are my suggestions:
For the caster specific rings (Canticle et all) I think they would be improved by increasing the caster's DC as the most frequently voiced complaint about casters is that the monsters do not take enough damage on the spells cast. More spells would be nice, more powerful effects would be better.
Litany (After beating the Vile King)
Only Useable by: Sorcerer
Improved Combat Casting
Legendary Spell Penetration (Beware custom coding required): - Plus 10 to caster check to beat creature's spell resistance
60% chance of 1x
30% chance of 2x
8% chance 3x
2% chance 4x
Legendary Spell Focus/Foci (Beware custom coding required): - Plus 10 to caster DC check to beat creature's save
Bonus Spell Slot of Level: Sorcerer: Level 7
Bonus Spell Slot of Level: Sorcerer: Level 7
Bonus Spell Slot of Level: Sorcerer: Level 8
Bonus Spell Slot of Level: Sorcerer: Level 8
Bonus Spell Slot of Level: Sorcerer: Level 8
Bonus Spell Slot of Level: Sorcerer: Level 9
Bonus Spell Slot of Level: Sorcerer: Level 9
Bonus Spell Slot of Level: Sorcerer: Level 9
Bonus Spell Slot of Level: Sorcerer: Level 9
My own contribution----
Isaac's Ring of Secrets (Beware custom coding required)
The legendary sorcerer Isaac developed improvements upon the simple magic missile spell thereby enshrining himself in the minds of caster's thereafter. Like all great ideas for offense, a counter measure is quickly developed. Low grade magical protections effectively eliminate the impact of IGM. Isaac, being a clever fellow, crafted this ring in great secret prior to his demise. The even greater surprise was that this ring indirectly lead to death of the item's creator.
This ring allows the wearer to mass the magic damage of an IGM spell into one missile that is delivered in a tremendous wallop rather than spread out over 15-20-30 (whatever the number) missiles. End magic damage increased by 30%. Multiple targets still splits the damage.
Each use stuns the wearer (20% chance 1 round) and costs 1/2 of available hit points. (This keeps the caster from spamming IGM). Dispells any Bigby effect on target. (This keeps caster from Grabby Handing and IGM hapless victims).