Here’s my list:
- Elven Charm (Chapter 13) plus a red or yellow Savior’s Staff (Chapter 3) lets you infinitely cast spells I think.
- Dwarven Hammer (Chapter 2) is cool if you get one that’s on-color.
- Royal Longsword (Chapter 2) casts a big damage spell when you match a lot of gems, if you had one then just running quadruple Channel would probably be viable.
- Guard’s Broadsword (Chapter 1) gives +power when matching colored gems, after looping a bunch it probably becomes insane.
You can also farm for spells:
- Green: Channel Poison (Chapter 1)
- Blue: Channel Ice (Chapter 13)
- Purple: Channel Darkness (Chapter 7) or Darkness (Chapter 15)
- Red: Channel Fire (Chapter 4)
- Yellow: Channel Light (Chapter 10). Smite is probably the best spell in the game but you can’t farm it specifically.